If your Bach's don't have any base, you should try checking your seating and speaker placments! You'll likely find that if there's not good bass from the speakers played full range(or even as small often), it's because you need to move things. The Speakers, or your listening possitions(or both) aren't coupling well at certain frequencies were they are.
Still, bass mangagement could be helping, depending on a lot of factors. I would concentrate on getting the mains set up for "full range" play(assuming you want to play em full range, and "filter free" possibly for 2 channel music dubties if you can), so they sound even and strong on their own*(relatively)..at least approaching flat frequency response. If you do this, your 2 channel music will have excellent potential(considering other acoustics).
You can still play the sub "in parallel" with the mains playing full range from your pre amp/amp set up, considering most moderate music choices. For the HT, hard rock, techno, and other heavy dynamic stuff however, bass management is going to be a must for best performance! In this case, I'd just run your mains as "small" looped through your "line-1" preamp from your digital pre/pro(you do have this, right?), and let the sub play from the "sub-out", playing the bass. So, you'd basically be using your DD/DTS pre/pro for HT/rock/heavy dynamic stuff, setting speakers to "small", and sub handles the bass. Then, for more pure music dubties, you can just bypass the pre/pro, and do full range for the Bach's, and let the sub play "in parallel. Infact, you can use the RCA connection on the sub from your DD/DTS pre/pro, and use "speaker level" connections for your music chores when played "in parallel"! This might be a bit tricky, but workable for excellent results if done right.
HOpe this helps
