Depending on how much you want to spend and if you want a tubed pre or solid state pre, I would consider at least listening to the SOnic Frontiers Line series or the Adcom GFP 750. They both have a HT bypass loop and work very well in 2-channel mode as well. I tried the whole calibration thing with a pre amp that didn't have the processor loop and I didn't like the fact that I couldn't control the volume of my theater in variations. Meaning, that if I wanted to hear the movie but at a lower volume inwhich I originally had it calibrated to, I would have to recalibrate my system just to turn it down to a lower level. I believe that Proceed and EAD makes some nice pre - pros that you might find used and at a fine price and possibly may give you the performance that you're looking for in a one box unit as well.
Good Luck.
Good Luck.