Re: Advice on speaker system purchase
No matter what you do, I think upgrading to any Ascend speakers from what you have will be a big and worthwhile upgrade. First off, the delta between performance of each speaker is really a personal thing. Certain qualities are much more important to some people than others (treble clarity, impact, dynamics, bass quantity/quality, imaging, etc) so it's impossible to slap a value on it that will be representative for anyone except that user.
The thing to keep in mind is that the RAAL tweeters are world-class pieces of engineering bliss. Nothing else I've heard has that level of clarity and accuracy while not being harsh or metallic sounding. It's a fantastic experience. The other dome tweeters Dave uses are also incredible and great performers which will sound fantastic over what you have. I just think the RAALs add an extra level that anyone can appreciate in any room. The other thing with the Sierras is that they are in beautiful bamboo cabinets with options for finishes, while the other speakers are much more utilitarian. So if looks matter to you in the long run, that is a consideration. I'm very happy with how beautiful my Towers are in satin black and I don't regret splurging for that at all.
As for subwoofer, that's all up to you and what you're willing to spend. Rythmik subs are always going to be tighter and punchier, but some people prefer a bit more flubby bass for games and movies because it gives you more of that wow factor and is closer to what people expect when a lot of bass is present. I think you'd be happy with whatever you can afford from HSU, SVS, or Rythmik, especially since you're in a smaller room for now.
If it were me, I'd spring for the Sierra-2 LCR, use the HTM-200's for surround duty (they're easier to place as surrounds, no rear port to contend with, and they match just fine IMO), and pick up whatever sub makes your budget happy. There's no real reason to buy a giant sub just because you might move to a bigger room one day. I'd say just get an FVX15. It has plenty of power for most rooms, and will work just fine in a bigger space, plus it'll hit like a truck in your small room and will be tons of fun. Keep in mind that it weighs over 100 pounds, though, so it's not like it's easy to move. If that is a concern you may want to go with SVS, as HSU subs also weigh a ton.
Ignore anyone who tells you you'd be happy with Klipsch in the long run. They are lying to you and themselves. I've been down that path and even the HTM-200's just walk all over any Klipsch speakers I've heard. Horns are just the worst for detail and imaging. Sure the soundstage is wide, but images are flat and boring and high frequency detail comes across like nails on a chalkboard when you compare them to any of Dave's designs. You're being charged $300 for speakers that cost maybe $20 to make, plus all of their marketing, sales, distribution, and normal markup to include. Dave gives you waaaaay more speaker for your dollar, no matter what way you look at it. I'm willing to bet that the crossover components in the HTM-200 alone cost more than the materials for an entire Klipsch speaker, drivers and housing included.
It's also important to factor in what receiver or processor/amp you're using. If you have an older or lower powered receiver you'll want to upgrade that as well, lest you underpower your fantastic speakers. If you need to drop more money on electronics, I would say it's fine to ratchet the budget down a bit and go with a decent receiver and a full CMT setup.
-Alex
PS4/Nvidia Shield --> Emotiva XMC-1 --> Emotiva XPA-5 --> Ascend Acoustics Sierra Towers and Horizon Center w/ RAAL tweeters (L/C/R), HTM-200 SE (Surrounds), 2x Rythmik F12 subwoofers