It is is quite likely that I'm going to have to move abroad again, for quite some time. Moving gear in between Belgium and France was easy but Toronto or Boston is a different business. It's not for tomorrow morning ( should be Fall 2015) but I'm already contemplating ways to simplify a lot my setup.
What I'm considering for now is a all-in-one USB DAC-amp for my HD650. On the digital side, I already have a pcb with pcm2707-src4192-pcm1798 I can hack (an old spare of my current DAC). I'll use a different USB receiver to have a 24bit input, to control the volume purely in the digital domain.
On the analog side, here's a possible solution. The I/V stage part of it works well, I'm using the same right now. The opamp feeding vcom is used to null the voltage at the input pins of the opa1632, or rather at the output of the DAC. The output section is nothing special but should be decent enough. It should hit 3Vrms when powered from +/-8v (to keep heat low, the opa1632 can get quite hot at higher voltages). It's enough in my experience with the HD650. With a src4192 upsampling everything to 96khz, in front of the pcm1798 with its 8x oversampling, filtering can be kept minimal.
I've drawn a preliminary pcb for a channel. It's 50*32mm, dual sided. All smd parts are 1206. It requires just one jumper running under the board, from the output of the DC bias opamp to vcom.
Obviously, comments on how to improve the pcb are more than welcome. In particular, comments on how to deal with the grounding of R5 would be useful. At first analysis, I'd run it by a dedicated wire to the star ground of the +/- power supply.