Is 57db gain enough for Dynavector XX-2?

Sorry to disagree with the others as well, but the picture that you paint in incomplete. The gain of the phono preamp must be added to the gain of the preamp to determine total gain. With a tube preamp with say 20db of gain, you will have a total of 77 db of gain, and provided that the noise floor in the phono preamp is low enough, this should do with the added gain of the amp. If your preamp is of low gain, or if your phono preamp has a high noise floor, then you are skating on the edge.

I would respectfully disagree that noise is the only consideration, I believe that dynamics can be compromised by a lack of gain as well.