Help and advice needed re: amp usage

Several years ago I jumped with both feet into HT. Ditched my two channel stuff and built a decent HT system. After all, they told me, the HT set up would work just fine for two channel music. Well, I've been heartily disappointed by two channel listening ever since. The brains of the system is an Integra (Onkyo) DTR 6.2 receiver. Speakers are DefTech all around. Here's my question . . .

The 6.2 is 100 watts/channel at 8 ohms. The mains (BP30's) have a power handling capacity "exceeding 500 watts." The 6.2 has pre-outs. Can I add a separate 2 channel amp only to the main r/l pre-outs to beef up the sound of the mains for 2 channel listening? (and leave the balance of the speakers attached to the receiver's amp for HT). I don't want to switch speaker connections when moving from HT to stereo. I have heard from several sources that the BP30s are very power hungry. If I can do this, and up the watts significantly driving the mains, will I see an improvement in sound? Particularly, I am disappointed with the thinness of the bottom end. Not a problem with HT due to the addition of a sub, but I prefer to listen without a sub for music.

If all this makes sense, and is possible, I would like recommendations for amps. How much power? What should I audition? My budget is more beer than champagne right now.

For what it's worth, I listen to 75% vinyl -- all styles of music.

Please don't flame the DefTechs or Integra, or tell me to scrap the system and start over. That's not very helpful and not possible right now.