My mistake. I thought you were talking about the No.39, which is a standalone CD player.
For DACs, I've been considering the Benchmark DAC1/USB, some used TUBE DACs ... but I have to include the budget for the digital cable.
FYI, My biggest improvement over many years is actually a pre-amp upgrade. I got so MUCH more out of the 3910, so I think I'll wait for now.
I don't consider modding the 3910. Too much $