Would Martin Logan Spires benefit from subwoofer?

I would normally say ML Descent because it is easily setup to go with your MLs most likely...But JL Audio is one serious sub.

In the end, with your room, if you can do 2 subs, many people say [properly set up] it is far smoother. And i can imagine that is absolutely right. So i would say 2 ML Depths.

agree!

Nice big room. I would say a well set up sub configuration will benefit even big speakers. I know many, many owners of Wilson X1s, X2s who use subs...probably which are cut off at 35hz or so...but there is a surprising increase in heft, slam and atmosphere that results.

I am a bass freak...but not bass, bass all over the place...but i just enjoy (even at low levels) feeling the quick tight punch of a drum bass thwack. I have a Velodyne DD18...cut off above 40hz...and it works beautifully.

takes a while to setup 'perfectly'...but its worth it. I also found an Auralex subwoofer isolation platform (60 bucks) helped incredibly!!! Good luck and pls keep us posted.