Seems like you have a very nice system already. I also have the MC202, its a rare and wonderful power amp.
If you're wanting to maintain a 'tube' sound, I don't think you'll get it at all if you run a DAC preamp directly to your power amp. It will be very fast and detailed but likely missing any tube-like warmth. If the C2500 is too pricey, you might consider the SS C48 which has a DAC. The C48 is an excellent built and sounding pre; I don't know if you're open to using tone controls but its been my experience when using the 5 band EQ on the C48, you can dial in pretty much any type of sound you want, from very forward and detailed resolution, to fat and full-bodied warmth.
I have a C48 and its the only piece in my system I'll never sell, and used prices are very reasonable for this full featured preamp.
By the way, how do you pllan to bi-amp?