I personally went with the Mythos 8 after having the 3 for a while, and I thought the upgrade was worth it. Since the majority of dialog for movies is from the center channel, having a better center is well worth it.
The L&R mains are great, but I've never been a fan of the integrated subwoofer. They sound decent, but not fantastic. If you have an amplifier issue, the speaker has to go in for repair and you lose a main speaker instead of just the subwoofer.
Meanwhile, with the Mythos 1 speakers, you save about $1,000 and you get more lower midrange and midrange speakers from the setup. A $1,000 sub is likely going to serve you far better.
As well, you will need to make sure that you have a power outlet where you want to put the L&R speakers to power them, as well as you will need to run a piece of coax cable for the subwoofer (LFE) input into each speaker. Both of these items are rarely in place where they need to be, but must be done for proper setup of these speakers.
Now, if you are prepared to get another sub, and have all the above, and the money isn't a huge issue, then I do believe that these are very good speakers. They certainly aren't a 'compromise' of a product overall, and their style is excellent.
For a receiver, I wouldn't consider a generation or two older model if it could be avoided. With more and more HDMI equipment coming to market, you would want a receiver equipped with 4 HDMI inputs all of which are version 1.3, and the receiver should be capable of decoding the newest high resolution audio formats (DTS-MA, Dolby True-HD). The Yamaha has none of this.
Instead, perhaps the Denon AVR-2809 might be an excellent choice, or look at the 1900 or 3900 receivers from Yamaha.
The Monster isn't a bad piece (IMO), but there are clearly options worth noting.
DO NOT BUY MONSTER CABLE!
www.monoprice.com
www.bluejeanscable.com
No matter what the sales guy says, if you're spending more than about $100 or so on the cabling, you are likely spending to much.