Subwoofers.... one 10" or two 8"?

Yes, 8" perhaps cannot be true subwoofers but they certainly can be true woofers, and this just could be enough.

I believe, this cannot be answered in general terms. There would be both advantages and disadvantages of both arrangements. Without knowing much about your preferences, your speakers and room, it really would be a very wild guess. But if you want one - I would go with two subs if you have enough room to correctly position them. The reason for this being that they should be able to better integrate with your main speakers, theoretically.

lars- 
Try both ways of hooking up your sub(s) and hear which sounds best to you.  I can run the SVSs with either high level or line level inputs.  I had thought line level was the better way to go (running floor standers full range and using a 2nd set of preamp out connections to the subs) but found a speaker level connection sounded better to me...thought things sounded "fuller".

In theory, if  you have the time and space to find the optimum location for the subs, 2 assymetrically placed subs will usually yield a smoother combined response.

Having said this, a 10" sub is a lot better than an 8". The surface area a 10" driver can move is close to that of 2 x 8" woofers, so distortion, low frequency and dynamic range all get much better with those 2 extra inches.

Looking at the review though, I would think an EQ is a better solution than a sub for you.  Or an EQ and a subwoofer. I'm actually really surprised to see measurements that show such a difference between the treble and bass (10 dB!) That's kind of huge. Adding more bottom end weight may be the worst possible thing.  The only way to tell is to measure in room though.

Best,


Erik

The two subs I'm looking at are the NHT Classic 10 and the Energy ESW8. Both of these have fully variable crossovers and they both have the black piano finish that would match my mains; not necessary but a bonus, all other things being equal.  Is there any advantage to connecting to the sub out of high level speaker outputs as opposed to going from low level preamp outs?

On several occasions I have demo'ed a wonderful 10" REL and 8" Sunfire. Both will fill the OP needs.

With all due respect to gdhal, I went with a pair of SVS SB1000 to fill out the bottom end from some Silverline Prelude Pluses.  The Pluses have surprisingly good bass for the size of their drivers.  If all I listened to were, say, acoustic jazz they would be completely adequate.  BUT things being what they are, I wanted a little more so ordered the SB1000s.  The Silverlines run full range and the subs are connected via speaker level input from amps.  The subs are positioned next to the floor standers and crossed over at around 100 Hz.   I listen about 8-10' from speakers that are 2-3' out from front wall in a ~19'x21'room with an open back wall (i.e., wall behind the listening position).  Subs disappear but give Tony Levin's bass a nice growl and make Bela Fleck's Cosmic Hippo sound amazing.  The system is posted if you want to take a look.  Good luck in your decision.

I think whatever you decide you want to go with one sub, not two. Here is one to consider: 
http://goldenear.com/products/supersub-series?gktab=1

Hi larstusor,

The 3dB-down point at 33 Hz on your Mirages give you some room to work with, so you might end up wanting to leave their signal unmodified and just "add" the sub(s) at a reduced output level, so to speak. Or you can think about crossing them over to the Mirages and reducing their burden if need be...either way would be ok. As for 8" vs 10", it may come down to a toss up, really...two eights might be quicker, but one ten should go deeper. As far as balancing the bass between the two mains goes, it all depends on what frequency range you end up crossing them in at. At about 60 Hz or below the summing of the bass effect will be pretty much nil. On up to around 100 Hz starts audibly introducing the summing effect and above that frequency it starts to become more and more obvious, IME.

Maybe the bigger question, especially in the price range you're considering, is just how flexible the integration is going to be with your mains. Maybe the number one reason for buyer remorse with subwoofers is not that they don't go low enough, but that they don't offer sufficient control over the right parameters to blend properly, i.e. invisibly enough. I'd much rather go with 2 eights that offer flexibility than any ten that doesn't. In fact, personally, as far as I'm concerned, a sub that isn't offering sufficient flexibility isn't really a sub at all...just a waste of time and money, really. If you can't find one of those in whatever price range you're considering, my advice would be to pass until you can maybe move up the ladder just a bit. That said, there are good ones out there. Just look at things like crossover frequency selections...the more individual settings the better...just 2 or 3??...you gotta hope like hell you get lucky with one of them or you're screwed. Digital parameters are worth looking for if you can find them, since they offer a good bit of sonic transparency in the bass region, usually without much drawback, especially if you're not crossing into the mains. But, you may have to either search a while longer for that or be prepared to move up the ladder.
 
Hope that helps