If it were me I would keep the speakers and get some better electronics. A great preamp is indispensable in a great system and I doubt running the M51 as a pre will be as good as a great preamp. If it were me I would take all the money you are willing to spend on the Studio 2s and get a better amp and preamp especially if you say you are already nearly thrilled with the sound of the 208s.
Revel or Aerial
If you had an opportunity to go from Revel F208s to Studio 2s or Aerial 7Ts, which one would you choose. The price is the same; therefore is not a consideration. I don't have an opportunity to listen to the Aerial 7Ts prior to purchase. My system consist of the following: Parasound Halo A21, NAD 565bee CD Player, getting NAD M51 to replace Peachtree Nova preamp, and Revel F208s.