subwoofer question

Check the NHT subwoofer close-outs.I bought the A1/X1/W1 system for my HT set-up.It is a very good subwoofer system.My friend bought the same set-up with the single woofer sub enclosures for his bass augmentation ,under the Merlin mxe.He complained a little about the transparency,but this shouldn't be an issue in a HT set-up (.1).He changed the crossover out to an LP-1 and is extremely happy.
The benefit of the X-1/2 crossover in a HT set-up is that there are a myriad of controls at your disposal:X-over freq,phase and boundary control.It also allows for use of two subs and additional routing for a summed/single unit.

Get a newer one, those subwoofer amps don't last forever. I got two (HSU & A/D/S)subs that both amps just stop working after a few years.

Hsu gives you a decent sound for the money.M&K subs are the easiest subs that I've been able to pinpoint their location in a room.

At $900 used in a manageable sized room like yours, for HT only use, I would definitely buy a more current single, large sub.

IMHO, a pair of M&K (or any other brand of) subs might make sense for a dual use system where twin subs can be used to smooth bass response without adding EQ, which some people find objectionable for a music system. For HT only, I'd use a single large unit and also make sure that I had Digital Room Correction capability (e.g. Audyssey) somewhere in the chain to achieve smooth bass response via EQ.

Just MHO.

Good Luck

Marty