Astro.
DSD on the Big7 is ONLY by USB. DSD and PCM engines are separate. PCM is R2R and DSD is "chipless" discrete decoder.
Perhaps the Golden Atlantic may be better suited to you (if you are not bothered about tube rolling)?
Not sure what SPDIF max is. I have only ever used it with spinners, but I guess with a USB/SPdif converter (off Ramp, etc) it could take HiRez PCM too.
Thanks wisnon. So next question would be I guess, how far behind is PCM on the current discrete board in the Big 7 to up sampled PCM - DSD using the USB input. My system is using SPDIF out from a Rednet AOIP and ethernet out from my server. I got a nice improvement dropping USB so not wanting to go back to that really.