Thanks guys. I kind of suspected what you stated above. As nice as the XDAs are for the money, I really do believe that they need a true pre amp. My XDA-1 doesn't put out nearly enough juice to drive my amp correctly.
I have been giving a tube pre amp some thought for quite a while. Unfortunately, I just don't have the setup (space) to get into tubes right now.
I recently ran across an Aragon 28K MkII pre amp. I really don't know what my fascination is with Aragon gear, but I've always wanted an Aragon pre to go along with my Aragon amp, so I grabbed it. It should be here tomorrow.
My present system has turned into such a budget build that I'm thinking that when I get to move into a listening room, I may just put another system together based on a tube pre amp. I've been wanting to try some Class D amps too and don't want to get rid of my Aragon.