Dual Subwoofers?

2 subs are great. I bet you'll hear from the DEBRA (distributed Bass Array) users, too.

Though, I would opt to using the amp outputs instead of the preamp.

Bob

2 subs much better than one.  A couple SVS SB1000 Pro subs will get you down to an honest 20Hz with minimal size at less than $1000 and absolutely transform your listening experience.  

Qty 2 Rythmik subs
F12SE-XLR3 piano black, A370XLR3 plate amp

I bought the second about 6 weeks after the first.

I’m still amazed at the difference after adding a second.

Overkill for your application but IME 2 is better than 1.

2 subs are better than one, and 4 are better than 2. Charge the room correctly and you will be rewarded with much more than just better bass, but with added clarity across the frequency spectrum and an expanded soundstage that will immerse you into the music. 

rhg3 I have the same dual setup