REL Classic 98

I would talk to REL. You may be able to stack their other subs as well. (you take the feet off and use a thin shelf liner pad between them),

You said you want to run 2 subs. It is NOT overkill when you stack them. Understand that you will gain a FREE 6db boost to the bass. (Yes! that's a big boost) "oh my! that's overkill in my room"! "too much bass"! NO, it requires you to now turn the gain control DOWN to achieve the same level of bass. It's not louder it's better for several reasons.

This lets each sub relax on a lower gain level. Turn the knob DOWN. Reduces cone excursion.The result is less distortion, cleaner more relaxed, effortless bass. Tighter, punchy. Also the amp works less on a lower level. Less distortion and longer life. Better in every way. 

One last point... stacked subs can have one sub set @40hz. and the other sub set higher to say @70hz. This gives a slight boost to upper bass region as well. You can't do that running them in stereo mode as there would be an audible imbalance.

So, 2 subs in stereo or 2 subs stacked? There's no question which yields a better sound. 

@gdaddy1 the t/9x has a downward firing woofer. So, clearly can’t take the feet off and stack it flush on top of anything.  But I’d love to br wrong and for REL to tell me I can stack those in some other way, b/c I’d buy another one in a heartbeat. I fear the s/550 is just too big to fit in that room. 

Kirkwallace,

You can hook one REL to two monoblocks. Ask 

REL technical for their diagram on how to do it. 

Some say you can't but I did it for years with an 

old downward firing classic REL and Quad II Forty

monoblocks. Good luck.

No, you cant stack downfiring subs. The goal is to get both drivers as close as possible.

REL isn’t the only game in town.. SVS are also stackable (as well as others). You should take 5 minutes and call them also.

If your not trying to achieve high level bass or it doesn’t mean that much to you then one sub will do just fine. You know the room and what your aiming for better than anyone here.

However, my point is, IF your going with 2 subs, shooting for the best bass quality, there’s no reason not to stack them vs. running 2 subs in stereo.

Make a few phone calls.

I have reached out to REL, @gdaddy1 . No doubt stacked S/550s would sound better than 2 T/9xs on the floor, and they would take up less floor space.  So, perhaps that is where i will end up. The monoblocks are scheduled to arrive on Tuesday, so i can start experimenting with the single T/9x then and decide whether that sound is unacceptable.

thanks, again.