You don't mention what video display you use - if you use a RPTV with the L/R's flanking it on the front, one of the biggest things you could do would be to either switch to a front projector / retractable screen, a plasma screen, or somehow imbed the RPTV in the wall so it's flush. Any of these would allow the speakers to "breathe" a lot more when used for just music.
Undoubtedly there are dedicated preamps the will give you performance boosts vs. the Krell in analog pass-through, but that's a pretty nice system you've got there. I'm pretty avid about music and movies and have a single system as well (not all that different in scope and gear from yours), and to me it's not worth all the extra complexity you'll get from adding a dedicated preamp, etc. Your tastes quite possibly will vary, but it's nice to have a clean setup, and there's no overt weak point in your gear. I'd focus on environmental issues, starting with the TV choice, and go from there. -Kirk