Happy to help
The subwoofer is actually the easy part. There are quite a few really good, reasonably priced subs these days from the likes of Rythmik, SVSound, HSU/Outlaw and others. It's really just a matter of getting the model that has the output capabilities and extension that your room requires.
In a larger room, there's no question that a ported subwoofer is going to be more efficient and less expensive in order to get true 20Hz (or lower) extension with enough output to pressurize your space. With any sealed sub, it is entirely up to the woofer to move the air. It gets no help or amplification from a port or bass radiator. You can still have terrific extension and output from a sealed design, but it has to have absolutely massive amplification and a hell of a driver or drivers. If you look at the dual opposed designs used by Epik, what you'll find are sealed subs that have an EQ boost on the low bass frequencies so that the sealed subs still play flat down to 20Hz. The natural design of a sealed sub that has no additional EQ or filters is to have great output up around 40-50Hz, but to naturally start to roll off with a 12dB/octave slope below that. In other words, down at 20Hz, a sealed sub that does not have a built-in EQ will be 12dB quieter than it is up at 40Hz.
So sealed subs - like the SVSound SB13-Plus - rely on "room gain" to even the frequency response back out. Bass naturally reflects off of walls, ceilings and floors. The bass sort of "bounces around" your room, so the low bass gets amplified by this internal reflection within the room. When the room is larger though, the walls are further away and thus, the strength of the reflections are reduced. Sound waves get weaker the farther they travel, after all
So you get less "room gain" in a larger space and thus, the subwoofer itself needs to be able to maintain a flat frequency response to a lower frequency. Long story short, since movies are a large portion of what you watch and you have a large space due to the theater area being open to other rooms and areas of the house, what you want is a subwoofer that can maintain flat frequency response all the way down to 20Hz on its own - and a ported sub is the most cost effective way to achieve that goal.
Right at 20Hz, the Rythmik FV15HP and SVSound PB or PC12-Plus have almost exactly the same output. SVSound really went for very flat frequency response, so they basically limit the output of the their subs above 20Hz somewhat so that the frequency response remains very flat and linear. Rythmik, on the other hand, lets their subs "off the leash" a little bit more. As a result, that big 15" driver in the FV15HP can produce significantly more output in the "hit you in the chest" tactile region of 40-60Hz than it can right down at 20Hz. The FV15HP can actually get a little louder than even the SVSound PB or PC13-Ultra subs in that region, although the Ultra SVS subs have more 20Hz output and are flatter overall.
This stuff only shows up when you are pushing the subs to their absolute limits though. What you should take away from this is that you absolutely cannot go wrong with either the Rythmik FV15HP or SVSound PB or PC12-Plus or Ultra subs. They can definitely handle your room size, they can play flat right down to 20Hz (and even lower) all on their own, unlike most sealed subs, and they also both have excellent transient response and maintain linear output even as the volume gets higher and higher! They are excellent subs.
Of course, dual subs are almost always preferrable as well since you can use two subs set up in separate positions to garner fewer peaks and nulls and get a bit of extra output as well. For that reason, you shouldn't overlook the option of something like dual HSU VTF-15H subs, since their lower price point might allow you to buy two of them rather than just one. Whether dual subs is right for you depends on a few things. If you only care about one "sweet spot" primary seat, then a single sub with careful placement and a bit of EQ can be entirely satisfying. If you care about multiple seats though, dual or quad subs should be the goal. A lone sub will always have peaks and nulls at certain locations in your room and there's just no escaping them. So a lone sub is not a good choice if you have several seats that you really care about and want to have nice, linear, accurate response at all of those seats. Dual subs - just in and of themselves - are not a guarantee of better response at all of your seats though. You still have to be able to position them correctly, so if space and placement options are very limited, getting dual subs isn't always practical or beneficial. The other thing to know is that having two or even four subs doesn't increase the loudness nearly as much as you might expect. Multiple subs are more about evening out the frequency response throughout the entire room. You now have more sources of bass and that results in far more interaction of the bass waves. All of those bass waves and bass wave reflections interacting is what creates the smoother frequency response, but it also means that everything just sort of gets smoothed out, not louder. You can use two subs to get way louder by stacking them, but then you don't get any of the smoothing effect, so that's not the way we normally use multiple subs. We want the smoothing
Anywho, I don't mean to bad mouth the Paradigm Cinema or Def Tech Mythos speakers. They're not a "disaster"
But they have the problem I talked about where the center speaker is just an identical L/R speaker turned on its side - and that just doesn't work well at all. I tend to consider the performance of the whole system. Just a pair of L/R Mythos speakers sound pretty good! But when the center doesn't match and has bad off-axis response for anyone who isn't sitting dead center, I just can't get excited about that or be satisfied by it. Axiom has the same problem with their center speakers. I like the on-wall M22 and M3 speakers quite a lot, but their on-wall VP100 and VP150 centers kind of suck, so it's really tough to recommend them for a 60% movies set up.
One potential option that's only a little bit more expensive would be the Jamo THX D 600 speakers - they go for around $600 a piece. The issue I had with these speakers is I didn't get the best soundstage when listening to them. They were quite "flat" with no real soundstage depth. So to me, they weren't the best music speakers. But where they might make a lot of sense for you is that they can really crank out the volume. They are fully THX Ultra 2 certified, so they're designed to play quite loud indeed. And being that they are literally identical across the front three (no change in orientation, just the exact same speaker in all three front positions), pans across the front are perfect and seemless.
So much like the Revel or Goldenear on-walls, if you can audition them and get a full refund on a return, I'd say they're worth a look. I know you're wanting 40% music speakers as well, so the Jamo THX speakers might not quite float your boat. But I only heard them in store. It's possible they're capable of sounding better with music than what I heard. They are definitely capable of the output you will need though, so they have that going for them over, say, the Revels
