Hi Musicfile,
I think your idea of using an Ultra-Fi Dac will give you a level of space and fluidity that you would only get from a great analog rig comparably. Larry Moore, Ultra-Fi's chief designer is about ready to release his next DAC by the upcoming RMAF show. Ultra-Fi's new DAC has the most space and fluidity I've ever heard from any digital source (bar none). This is where most digital completely falls down IMHO.
Another improvement for your system is to change the EL-34 output tubes in your Dodd amps to JJ KT-77's. Both myself and others (who have compared the Kt-77's for their myriad of various branded El-34 amp varients) have found that the KT-77's completely smoke all El-34's, including the rare and VERY expensive NOS Mullard XF-1 and XF-2's (which is really saying something IMHO).
Lastly, you may want to consider Herbies tube dampeners on your input and output tubes too. My Dodd's bass resolution, tightness, image stability and image focus greatly improved with the Herbies.
Another (very costly) mod to consider is using RSAD's Althiest power cables on your Dodds, which was such a sonic improvement that I was greatly surprised how the amps gained a whole new level of refinement seemingly everywhere; sonically speaking ;-)
