Spectral DMC 10 Differences & Upgrades

Does anyone know the differences between the versions of the Spectral DMC 10 preamps, especially the DMC 10 Gamma and Delta?

What upgrades or refurbishing can be done to this preamp? I have heard of Caps being replaced by the factory. Is there anything else they can do to it? Does anyone know the cost involved with doing these upgrades?
Thanks for your help, I am seriously thinking of buying a DMC 10 Gamma.
Joe