You did not specify if you wanted to go tube or solid state?
I'm a fan of tube pre-amps, but I would not necessarily suggest it for your setup. In a combo system, using bypass, the dedicated 2-channel pre-amp would be used any time the system is in use for either 2-channel music or HT. If you used your system for TV, you would have the tube pre-amp on a lot and decrease the lifespan of the tubes significantly.
Now, if you don't use the system that much, or if the cost of the tubes in the pre-amp doesn't bother you, go for it! Otherwise, consider a solid state design.
I too have a DV-50 and an HTS 7.1, and have heard good things about the Audio Research LS25 MkII. It has a HT bypass. I have never tried one though.
I have also tried several other Pre/pros and from my experience, the HTS 7.1 is one of the much better ones at two channel...not that there couldn't be better -