Subwoofer for two channel system

Hi,

I'm currently using Totem Lightning for my two channel system wand I'm satisfy with the soundstage.

Danny

I also have to of VSA VRS1 subs with my VR4 Gen III HSE. Sound awsome, you can't go wrong with it. Good luck

Vandersteen 2w or 2wq. Virtually transparent.

The VBT (aka TBI) Magellan VIII is another good option that meets your criteria. Very tuneful bass that doesn't get in the way, and has a small visual impact.
I'd recommend a pair if you can swing it, and place them in the corners. I believe they have powered ones but I used a separate bass amp (with my Tact crossover).
I eventually replaced them with RBH subs (also very good, but fairly imposing visually) because I wanted to move more air and set the crossover higher. The VBTs however, were a bit quicker and more tuneful.
IMHO, stereo subs is the way to go, with a separate amp using speaker level inputs (an amp vibrating in a sub box--not a great idea).

I'm beginning to sound like a broken record, I know, but you really do owe it to yourself to check out the Digital Drive series from Velodyne. Amazing subs!

Tom.