Single vs Dual Subs

Lou,

A-gon'r Kr4 has compared many of the available room correction devices (not sure about the SVS) in his work for Stereophile. You might want to drop him an e-mail.

IME, The Velodyne requires some time/effort. The process of flattening the FR is a lot less logical than you might think - sometimes it feels a bit like a game of whack-a-mole. However, the SMS is very flexible and it will get you there, eventually. Also, you can tailor/tweak response to taste, which may prove useful. The thing works as designed and it's fairly priced. That noted, KR has indicated in previous threads that he prefers Audyssey, as implemented in the Audyssey powered devices to which he's compared the SMS.

Marty

PS The SVS requires a x-over ahead of it (so budget accordingly), while the SMS includes a built-in x-over. Alas, if you require low cut for the mains, the built-in x-over in the SMS will subject your main speakers' signal to ADA conversion. I found this audible (I think), but "benign" - it sounded SLIGHTLY different, but not necessarily "worse" than the non ADA signal. Nonetheless, it bothered me in principle, so I added an NHT X-2 ($300) to low cut the mains.

For the money ($450 at Audioadvisor.com), I can tell you that the SMS does a great job - particularly if you're not acutely stricken with audiophilia nervosa, like me.

I know I'm late to the party, but must chime in.
Bass below 80hz or so is not localizable. Unless your room is HUGE.
The advantage of double subs is reduction in standing wave peak/null situations.
Subs located asymetrically will tend to cancel out each others standing waves producing a more uniform in-room response and a larger sweet spot....which is important for HT duties where a crowd may show up.

Budget is around $2k (...) you could get a pair of new subs from Hsu Research...

That is the answer to your query, IMO.
Not perfect but good performance. Start with placement on the same plane as spkrs & take it fm there.

To Bob's point on EQ to 300 hz.
This is obviously room dependent. Every listening room I've had (and measured) has had obvious issues below 150hz. IME, above this point (including the falling treble response I usually get above 10khz), room effects are still present, but much less severe/troublesome. Between 80ish hz and 150ish hz, room treatments (hemholtz resonators or "Bassbusters") have proven very effective in my efforts to "clean up". Below 80ish hz, it's either soffit or EQ, unless your room is large enough to approximate an anechoic chamber.

My bottom line: I can usually live with the "bottom end" room effects between 150hz and 300hz, "resonate" them away between 80ish and 150ish, and EQ them below that. This is just my preferred solution. FWIW.

Marty