You're very welcome!
Decoupling your subwoofer and speakers is an absolute must, IMO. The Auralex products are not that expensive and they do a terrific job. The GRAMMA in particular is just an excellent value, IMO.
I know that there are many people around here who like to debate subwoofers. They will point to all sorts of measurements and anecdotal evidence in order to "prove" that one subwoofer is better than another.
In reality, the sound that you hear is a combination of the subwoofer's output and the room's interaction with that subwoofer. The room plays basically an equal role in the final sound that you hear. As such, the only comparisons of good subwoofers that can really be made are measurements taken in an anechoic chamber!
The simple fact is that human hearing is really not very good when it comes to bass frequencies. We have a very hard time distinguishing distortion from the original output, we almost completely fail at localizing where bass is coming from and in terms of audible detail, we are far more likely to process cues from the harmonics and higher frequencies rather than the true bass frequencies themselves.
Basically, what I am saying is that once you reach a certain performance level - where output is consistent and flat down to the lowest notes of human hearing and distortion of the actual output is kept below a certain level - talking about one subwoofer being "better" than another is really just splitting hairs and more often than not, comes down to expectations and presumptions rather than actual audible differences. When people WANT to hear a difference, they do! So that is why you'll see people swearing that HSU is better than SVS or that SVS is better than HSU or that some other brand like Epik is better than both of them or on and on. The bottom line is that they are all at a similar level of very good performance and while there may indeed be measurable differences, human hearing becomes the limiting factor and in a true, blind test, things like where the subwoofer is placed in the room, how it is set up and the orientation of the seating are going to make a MUCH larger difference than the comparative output of these various, good subwoofers.
If you are willing to increase your budget, all sorts of possibilities open up. That is a big reason why making a final decision can be so difficult!
My honest advice would be to keep your budget in mind and stick with the CBM-170SE speakers. The CMT-340SE really are suited to a larger room. They are designed with a wider horizontal dispersion and the MTM design means that you get a comb-filtered response in the vertical dispersion. Our brains are excellent at ignoring comb filtering, but when you have hard floors and an untreated ceiling, vertical reflections play a big part in how clear or muddy things sound.
Bottom line is that the CBM-170SE speakers are better suited to your room. They are also better suited to a smooth and effective cross-over to a capable subwoofer.
If you are willing to up your budget a bit, I would spend that money on a HSU VTF-2 MK3. Compared to the STF-2 that I previously recommended, the VTF-2 MK3 simply plays lower. While the STF-2 begins to roll off at around 35Hz and is down 3dB at 25Hz, the VTF-2 MK3 can reach convincingly down to 20Hz to give you genuinely "full range" sound. The VTF-2 MK3 has the handy attribute of also being the exact same dimensions as the Auralex GRAMMA riser - so they are a perfect fit for one another
There is always the temptation to spend just a little bit more and hope for just a little bit better performance. I'll be blunt with you and let you know that actually hearing audible differences is a much more subtle matter than most reviewers and audiophiles make it out to be. Are there audible differences to be had - improvements? Yes. But in truly blind tests, where people are not influenced by their expectations or there pre-hand knowledge of one speaker being more expensive than another, it turns out that our ability to hear genuine differences is not nearly as good as people believe. All sorts of other factors come into play and the speakers themselves matter less than things like how tired you are when you are listening, or how much you are focusing your attention on a particular note or voice.
Your at a great point where you have a decent, but still limited budget, some experience with entry-level equipment and a strong desire to really see how far this whole audio quality thing really goes! What I recommend most at a point like this is to stick to your budget and buy equipment that really delivers the tried and true, scientifically sound principles of good audio. Flat frequency response, even and rolling decay as you move off axis, low distortion and capable dynamics and output. These are the exact traits of the Ascend speakers and HSU subwoofer that I am recommending and that is why I recommend them so highly.
What I am trying to establish for you is a base line. Something to which you will be able to compare all other speaker set ups from here on out. Are these Ascend/HSU speakers the final word on audio quality? No! Of course not. But what they are are scientifically sound, accurate speakers that will really reveal to you what accurate sound is all about.
From there, you can really start to open your audio world. From this sort of design and quality level, things are all about refinement and, to be honest, character. More and more, what you will find is that speakers are often not voiced to be genuinely accurate. Instead, they are voiced to offer something "different". Something distinct that will catch your ears' attention.
But I like to start people off at a solid base line. Get to know what a really flat and linear set up sounds like and from there, it becomes much easier to start picking out the much more subtle nuances that will either suit your personal preferences or not
Edit: Forgot to answer your question about corner placement of the sub. In general, what happens as you move any speaker closer to any wall is that the low frequencies get reinforced (made louder) by the reflections off of the wall and by the wall itself vibrating in sympathy with the subwoofer. The problem is that, as I said, now you are hearing more of the room's interaction with the subwoofer, rather than the subwoofer itself.
For movies, pure loudness of output was often the goal. When the only bass you're hearing is a the rumble of an explosion, it doesn't matter all that much if the rumble is room resonance or genuine subwoofer output! But if you are listening to music, such room reinforcement causes the bass to sound muddy and indistinct.
When you are using a single subwoofer, the very best placement is actually out into the room at a position that is about 25% of the room's width away from the side wall and about 25% of the room's length away from the front wall. But this sort of placement is not usually feasible because that would put the subwoofer out into the room! Most people want to keep the subwoofer to the perimeter of the room. When you do that, the best placement is often about 1/3rd of the room's width away from the side wall with the subwoofer up against the front wall.
Usually, you will have a few places in the room where it would be aesthetically and practically acceptable to put the subwoofer. What works well is to actually move your seat out of the way and put your subwoofer in the spot where you would normally sit. Now play some bass sweeps or bass heavy music. Go squat (so that you are at your seated height) in those candidate positions. You will find that some sound loud and boomy, some sound much more quiet and hopefully, some will sound quite even, smooth and articulate. Switch positions now. Put your subwoofer at the spot where the bass sounded best and go sit back in your normal position
