Yes, but instead of using the pre-out on the tuner-preamp why not just use the tape out facility it probably has? Fixed output like your cd player, bypass the volume control of the first and probably sound better.
I can't think of any reason it would not be safe. Turn the volume down on the Adcom to begin with and then turn it up as high as you need. I assume the Classe does not have tone controls, so here is no risk of accidentally doubling up on bass boost or anything like that.