Re: Surround Speaker Choice
Warning: long.
There are multiple schools of thought on the importance of speaker matching in HT.
School #1, the purist position, espoused by THX and many of the people who originally designed surround sound, is that all five (non-subwoofer) speakers in 5.1 should be identical. It's the only way to be sure that when things pan from speaker to speaker that everything still sounds right. For example, all five speakers should be S2-EXs.
School #2 is that they don't all need to be identical, but they should at least be timbre-matched. Relatively small differences in efficiency and such between different speakers from the same line are pretty easy to compensate for with small changes in volume at different speakers, and modern HT processors that use room correction do this automatically anyway. For example, RAAL Towers for mains, RAAL Horizon center, and Lunas for surrounds.
School #3 is that they don't all need to be timbre-matched but they all have to have similar frequency response. If you have darker speakers in one position, you have to have darker speakers in all positions. This gives you a lot more flexibility in choosing brands/designs, since anything reasonably close will be fine, you probably won't be able to tell the difference anyway. For example, RAAL S2-EX mains, CMT-340 center, some good neutral surrounds from someone else.
School #4 is that it doesn't really matter—what's coming out of the surround channels is mostly just fill-in effects anyway, so as long as you have speakers, no worries. Example: CBM-170 mains, Polk CS10 center, NHT SuperZero surrounds.
So, which school is right?
Honestly I think it depends a lot on what you're listening to and how it's mixed. Advocates of schools 3&4 are correct that that some material, particularly movies/TV that don't emphasize sound, the surrounds aren't doing a lot. Advocates of positions 1&2 point out that there is material that really aggressively uses the surrounds and you pay a real penalty in the immersion experience in those cases when there's a mismatch.
I recently upgraded from a School 2 system to something very close to a School 1 system (the five aren't identical, but 3 of them are and the surrounds are very close to the front 3) and for stuff that really heavily uses all five channels (e.g., The Dark Side of the Moon in 5.1, some really well-mixed movies and even TV), it makes a difference.
Pairing something like HTM-200s with Ascend RAALs is kind of a 2.5 position. They're not perfectly timbre-matched but they're also more than just "similar frequency response." They are designed to go together and while they won't give you the full School 2 experience, it'll be pretty close.
It's also a function of your room/budget and what you listen to. Not everyone can actually put 5 exactly-matching speakers in their room, especially towers. If you listen to a lot of two-channel music, there's a real argument for sinking more money into the LR mains than into the other three speakers. If you listen to very little two-channel music but do watch a lot of movies/TV that are dialogue-oriented, maybe a little extra in the center channel makes sense. YMMV.
So, will it overall sound better if you get S2-EXs for surrounds? Yes. Is it enough better to justify the additional expense? Depending on what you listen to, it might not be. Since you have a sub, Lunas are going to do the job almost as well as 2EXs and are cheaper and easier to place.
If you're not going to perfectly timbre-match, there's not going to be enough difference between the 340s and the 200s for it to matter much. I keep saying it, but the 200s are really great speakers (especially for the money) if you have a subwoofer, which you do. They're also smaller and easy to place than the 340s.
So, I'd say you have four reasonable options:
* The School 3 (maybe 3.5; I'm not sure how well the Polk matches the 2EXs): just get a pair of HTM-200s. Con: still not a great match all the way around, but if you're living with the Polk center anyway it's probably not a big deal to you. Pro: super cost-efficient.
* The School 2.5: get a pair of 200s and replace your center with a RAAL-based center (probably a Duo). Con: more expensive than the first one. Pros: still cheaper than a new pair of EXs, definitely better sound than the School 3 option.
* The School 2: get a Duo center and Lunas for surrounds. Con: a couple hundred more than a pair of new EXs. Pros: beautiful timbre-matching (and appearance-matching; high SAF) all the way around.
* The School 1: get three EXs, one center and three surrounds. Con: spendy. Pro: perfect matching all the way around, as the purists intended it to be.
If I'd already budgeted for a pair of EXs then the S2.5 and S2 options are where I'd go—do you want to be a few bills under-budge or a few bills over-budget?
Luna Duo V2 LR, Titan Horizon V2, and Rythmik L22 & L12 in HT, Sierra-LXs in study, S-2EXs and Duo V2 C in bedroom, S-1 NrTs in dining room, S-1s at work, HTM-200s in kitchen. Brother owns CMT-340s and dad has a pair of CBM-170s.