You did screw up. The Carnetix is not an ATX-compliant PSU. It provides a single regulated voltage (user-selectable).
I'd see if you could return your Carnetx (or possibly resell it) and get a beefier Opus unit or a DSATX or an M2ATX perhaps.
IMHO, the PicoPSU is suspect in my eyes. I think you'd be better off with one PSU that does everything you need, including statup/shutdown, voltage regulation, etc.... Just liek your Opus did.