The one I settled on for those requirements was the VTL TL 2.5. (New around $1.5k, used for $8-900-ish). Gives you a nice little tube preamp with both a processor loop and a tape loop. Oops, re-read the post, and the VTL is single ended.
If all you're basically looking to do is integrate a 2-channel system with a HT system, all you really need is a HT processor or receiver with preouts for the main channels and any old preamp to suit your tastes. You then run the center and surrounds off of the HT setup as normal and merely run the preouts from the processor into any old input on the 2-channel preamp. If you have a tape loop or a processor loop on the preamp (which are electronically the same thing by different names) you can run into the preamp there, but you don't really need it -- all it does is make operation simpler by bypassing the volume control on the preamp and running straight through onto the amp for the main speakers.
If, on the other hand, you are running into the preamp at another input (we'll pick the AUX), then the main's signal from the processor will be running through the volume control of the processor (which is what you want) and the preamp (which is extra). To compensate for this, you'd have to set the volume on the preamp to some benchmark of your choosing (preferably zero gain, if you know where that is) and then balance the channels at the processor from there. Running through both volume controls will possibly cost you a slight bit in fidelity and adds the extra step of having to police the volume on the preamp (especially when you switch back to two-channel, so as to not treat yourself to a nasty surprise), but is otherwise a perfectly viable way of integrating the two systems.
I started with the VTL pre, with both a tape loop and a HT processor loop, and it was simple and easy. Then I switched to a Rogue, which has a tape loop but not a processor loop, and ran my HT processor into the AUX. While the pre was actually at Rogue (for other reasons) I talked them about installing a HT processor loop. He said he'd be happy to do it (for fairly cheap) but that he really didn't see the point or think that it was worth while--so I didn't bother. Now I'm running a Plinius pre (an electronically upgraded CD-LAD Mk.1, but without the processor loop hardware included on the Mk.2 frame) and am running the HT mains in through the Line 2 input. Now, this would normally be perfect but for the fact that the remote control frequency for my HT receiver (Marantz) and the Plinus's volume control are apparently the same (damn, damn, damn) so that every time I want to conrol the volume of the HT reciever it ALSO changes the volume of the Plinius, thus throwing it off of the benchmark and ruining the channel balancing of the Marantz. This is basically the ONLY reason I can think of not to have a processor loop, it is exceptionally unlikely, and, wouldn't you know it, exactly what happened to me.
To conclude my ramble, you could make due with any old balanced preamp you liked the sound of--the convenience of a processor loop, while a preference of some, is by no means a necessity. A processor (or tape) loop under $1k (used) should be easily doable. Balanced plus a processor loop under $1k may be a lot harder. Depends on which you prefer. But, I guess I'm just trying to explain (however inartfully and long-windedly) that you may not need both--above all, pick the preamp you like best based on its sound, the integration issue will be doable. Best of luck.