I have mentioned that in PM to iFi, but I want to repeat myself here. The iDSD sometimes stops outputting analogue signal to RCA outputs. I had that feeling that it usually happens when mode is changing either to/from higher sample rate or PCM - DSD - DXD. One may try to turn iDSD off and disconnect USB cable for few seconds, plug it to different USB port in your computer and then connect it back and turn iDSD on. This helped me most times. Also playing DSD128 material in Foobar and then switching to PCM sometimes helps. Also helped if I rebooted in Linux and used Jack at 352.8 sample rate, play some tack, and then then restart Jack at 44.1 sample rate, and stop Jack and reboot in Windows.
For me it sounds like iDSD supports hardware volume control or mute function and that get stuck in some memory of iDSD, or I also thought maybe PCM and DSD are decoded by two different DACs and the switching between them sometimes sticks. I have also had situation that Foobar was able to play DSD128 file fine, but couldn't switch back to PCM. I had rebooted the box several times then, with no success, I booted in Linux, then in Windows and finally I got it working again.
sounds like a windows problem to me.
hopefully you'll be able to figure out the issue...