Well, so far most of the people I see knocking usb or touting it's inferiority typically have some dog in the spdif side of the fight -- and the same goes for the other side as well.
The AMB gamma1 or 2 dac may be able to be configured for spdif to usb, and it is certainly technically possible, but why go from one, typically jittery medium to another -- I think the lack of devices is that by now most people are tending towards using computers and not spinners as transports, and when well designed the usb option is typically far more clean than an after-market spdif card, and easily better than any spdif capability that may be on the motherboard.
The field is moving fast and what was state of the art 3 years ago is kind of ho-hum now, and for the most part the dac chips are the same -- it's the support chips, software, receivers, power supplies and voltage regulators -- and how to use all these together that is really making the difference.
When I got my original Tranquility dac a few years ago, even though it used an old 16/44.1 nos chip, it was the first time I ever heard how much information there really is on a redbook cd -- and I had heard the best of the best EMM Labs, Audio Note, and other dacs available up to that point, yet this plain jane little redbook-only nos dac just brought more music out of a CD than I ever knew was possible. And now my Metrum Octave Mini (which uses industrial, super high-speed NOS telecomm dac chips and a spdif interface) blows the Tranquility away and offers hi-res as well.
The things that John Swenson seems to be doing with the BH dac and especially it's spdif interface look to take all this to an even higher level. So, as I originally said, it's very hard to generalize about anything in digital audio -- there are no absolutes, everything is in flux, and the best advice I can give anybody is to take each piece/system onit's own and don't discount anything based on interface, resolution, chip used, etc.
-- Jim
