Preamp for both 2 channel and Home Theatre

Try a Theta Casablanca I or II. In the $1500 -2500 range, the Theta offers excellent analog section and superb digital performance. Unlike the competitors, upgrades can be done as desired without having to replace the preamp/processor. Good luck!

Get a used Parasound Halo C2. Excellent 2ch and HT performance. I have the C1 (pretty much the same electronics and I am VERY satisfied.
Although not current, for older equipment, the Proceed AVP2 or the Aragon Soundstage are highly regarded and still worth consideration. Great bang for the buck!

VTL 2.5 and 5.5 have a surround processor pass through so you can operate both ways. Both under $2500 used.

I'll second Rkeman's suggestion that you consider Theta. I went from 2 channel to a Theta Casanova processor and Theta Intrepid 5 channel amp, and I'm real happy... if any of us can truthfully ever say that. The Casanova has two advantages over the Casablanca. It's way less expensive than the Casablanca, and has 24/96 processing where most of the Casablanca's don't. However, the Casablanca's analog might be better than the Casanova's. I mainly use my system for Stereo. I'd really like to know if the Casablanca's analog is superior to that of the Casanova.