One Sub or Two?

I went with F12SE Rythmiks because of the ability to dial them in variably (rather than 0 or 180, as the case is with REL subs) to a pretty tricky room. I got a pair. Love them. I have an older REL, too, and it is my third sub. The subs are coordinated using MiniDSP (link is about subwoofer integration).

Again, REL has a huge fan-boy contingent but not many models have variable phase. REL has 0/180, mostly.

A simple 0/180 switch allows for a complete reversal of the subwoofer’s polarity, effectively inverting the signal. But variable phase control on a subwoofer allows you to fine-tune the bass output to blend seamlessly with your main speakers, maximizing bass response and avoiding cancellations at the crossover frequency.

Two REL's, which ever models you can afford.

I have several systems and they all have two REL subs and I'm very happy with them.

Information about the size of your room would be helpful.  Based on the speakers and the HT / 2 channel mix, assuming a larger room, more is better.  No need to stop at two.  Highly recommend Rythmik servo subs over REL.

This info is all super, very appreciative!

Edit to include:

1. Room is not dedicated listening room, various wife-driven things like couches, coffee tables, lamps, etc. and is approximately 30Wx40Dx12H.

2. I normally use a sub for 2 channel listening as the B&Ws don’t quite cut it to my ears.  They excel in the midrange.  More important to me to have the music sound as correct as possible than the HT listening experience.

Again, many thanks!

1) most definitely two. evens out the response, increases dynamics and avoids localization.

2) I had two REL T9i and they sounded very good but missed the really low end notes and authority I did not know existed until I tried the SVS SB 3000. The SVS SB 3000 is a wonderfully musical sounding subwoofer with that really low end power and authority that makes it a real subwoofer and an exceptional value,