One Sub or Two?

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,

30x40 feet? Start saving for S class RELs.