You posted a good question. Unfortunately noone seems to have an answer for you. The best I can tell you is this:
I have an Arcam FMJ139 and a SB3/VDA-2/VAC-1. Both are great in their own right to the extent that I never thought of combining the 139 with the VDA-2. I also don't think that the 139 would benefit. The FMJ139 replaced a DV137, but that does not change my assessment. The DV137 is pretty damn good, too. The DV78 might benefit from a DAC upgrade or not. I am not at all familiar with that model. Personally, instead of trying to enhance the DV78's CD playback, I'd team the VDA/VAC with a Squeezebox, and use the DV78 for movies, only.
