I have been furthering the design somewhat more.
For the rabid (yes, that's you WM), I am considering separating L/R channel power regulators, although I have a designed-in option that allows you to run both channels off a single pair of regs should you not be rabid.
I've also been working on the board layouts with reference to how the devices are pinned, and have come up with a pretty clean layout in my head. Translation to PCB isn't a problem, although I've not looked at the digital part of the PCB yet. However simplicity is good.
Something that may surprise people when I finish up the design is how small the main DAC board will be. This is a very deliberate design feature to keep all paths short, and keep any track or plane resonances to extremely high frequencies.
I also thought I might make clear the design concepts here.
1) Scalability. Build this DAC how you want it... you can have separate power to each channel, unbalanced and balanced outs, loads of ins. Or you can have one input and one output, with shared power not only between channels but between digital and analogue sections.
2) Performance. I am designing this in such a way that if you go for the full monty of specification, performance should be very good indeed. If I can improve significantly (note: subjective) on my best modded superDAC (Will's) then I'll be happy.
I can see that the utterly insane can end up with a 4 box DAC (3 psus and the DAC). You can put everything into the same box if you want, but I'd go for at least two boxes.