Hi Steve,
So the answer to your original question is "Yes". There should not be any issue. And you should hear some improvement by replacing the pre/pro with a better preamp. What types of tubes will go into the DAC and the pre? Most NOS tubes, meaning tubes that were made in their golden days, will sound better than current productions. Different manufacturer will have different house sound as well. There have been some decent tubes coming out of China and Russia recently. I have not compare them to my NOS stash yet, but they will typically cost less, and are more accessible.
What music file format are you streaming? That may also impact SQ as well.
FrankC