In regards to feedback on on tube swapping, I put a vote in for the Amperex Bugle Boy 6922/E88CC's. I tried the stock tubes and the Siemens 7308's that Upscale Audio recommends. I find that the Amperex has more midrange warmth than either. Of course, I am running a system with a Solid State Amp so additional warmth is a priority for me. If you have sufficient warmth (existing tube Amp) and are looking for a tighter bass, I think the Siemens would work well. In either case, I would recommend trying something in addition to the stock tubes.
One little thing that has really helped out is the inclusion of the CD remote. It fits my hand perfectly and it has allowed me to skip purchasing an expensive optional ($500) remote with my pre-amp.
The only thing I can think of that would improve on the current edition is the removal of the Marantz CD4000 face plate and add a custom AH! one. I know it is kind of shallow, but it looks kind of funny having all high end gear along with a marantz CD player. You are constantly saying "No, its a tube Mod - really!".