Is two Subs better than One?

2 Subs Sound better to me. After all the opinions I thought I would buy a second DD15 Subwoofer. After setting it up but not yet finely tuning it; the volume needed to be decreased to synch with my Wilson 7's. I could definitely sense a fuller better balanced base. The mid and upper frequencies were more focused due to the fact that base appeared to fill the room better. With the base originally localized more to one side, the Wilson midrange on the opposite side did not feel as intergraded.
I guess bigger is better.

how do you hookup 2 subs to a preamp or processor?

I added a ACI Titan II LE as the second sub to my system and I don't think I will ever go back. My room is 13.5 x 17.5 and the second sub just make everything sounds better from 2-ch music to 5.1 HT movies. I'm using Anthem processor which has 2 sub outputs so hook-up is very easy.

Lynhnn, just curious, but at what frequency to you cross over your subs to your main speakers?

The default THX is 80Hz which can be customized to a diff number by the Anthem setup menu. I have tried various frequencies like 50, 60, 70, 80,90 ... and for my front speakers, I set it to 70Hz for music mode. I set it 80Hz for cinema mode. For other speakers in the system, I just use THX, which is 80Hz.
If you have large front speakers which can handle low frequency without distorting the sound, you can have it lower to 80Hz. Or if your speakers are so small, 100Hz can be set so the sound is cleaner.
If I have one sub, I would try to set it around 60Hz so more bass can be pumped out at my main speakers. But it again depends on how low the speakers can handle.

Cheers,