Do I need a subwoofer? Which brand and model?

I have OPPO BDP-105 , I think you will be happy with HSU-VTF15H. I am very happy with this.

Hi there.

1. Agree to buy quality now and 'double up' later if you wish.
2. I would think if you are able to get a powered sub, that will allow you to try to blend the 2 speakers using the crossover...or run them in parallel. I have played with Celestions and SF Guraneris and subs...and eventually found that running in parallel seemed to work for me despite its own imperfections due to the extension of the satellites.
3. If you are going to try an amp...i always like trying a brand whose sound i like...and go a bit higher up the chain just to see if the effect you are looking for is possible...and then back down into the price range. Because if the bigger models still cannot deliver what you want...then you've saved yourself a lot of time trying to audition a particular model(s) seriously. Parasound, Bryston's newer stuff, NAD make good stuff.
4. Between HSU and SVS, hard to say. I think both have good reputations. SVS is known (i think) for tremendous bass power/$. But a lot of people with music only systems stick with HSU as well. Gut tells me the ease/flexibility of setup will matter more here, and there you are going to have to investiate the speicific models in your price range and see which one allows better setup options.
5. Finally, regardless of which sub you go (or amp), if you can isolate the sub from the floor...i often find it makes a big difference (usually a good one) in terms of deliver clean bass that is not being 'echoed' by a wooden or vibrating floor.

hope that helps...keep asking if you have any other questions...

"The setup is in the living room, with three walls, and the fourth side open to the dining room. The living room itself would have been 18' L X 12' W X 18' H = 3888 cu. ft, but the fact that it opens up to the dining room makes the entire space more like 40' L X 18' W X 12' = 8540 cu. ft. Would I benefit from a subwoofer and which one should I get?"

I would first get a more powerful amp for your main speakers given the size of your room. You're NAD is good in that it jumps the amp and preamp section externally using rca jacks. It can be used just as a preamp. For subs, I would consider getting 2 small powered subs that are designed for music and not HT.

Thank you all for your comments, all of which are very helpful. I will definitely try adding a separate amp down the line and using the NAD I have as a preamp - I'm glad that is possible. Lloyd, I will take you up on raising the sub - that sounds like an interesting and worthwhile thing to try.

I still am debating SVS SB 2000 vs Hsu VTF 15H vs Hsu ULS 15. My needs are music oriented rather than HT. Any comments specific to these three choices for music rather than HT would be most welcome, to help me with my decision. Thanks again all!