You have to hook up the analog outs from the ERC to the multi-channel analog inputs on your Onkyo to get the best sound. I think the main problem people have is that they see the "CD" analog input on the back of their input and automatically plug their CDP in and think it's the best option while in reality it's not because AVR is then doing an analog-to-digital conversion and then another digital-to-analog conversion which worsens the sound. To get the most out of better CDPs (ones where the DACs are superior to whats in the AVR) you have to hook them up to the 7.1 outs because there is no processing going on at all and the signal remains untouched. In short, the ERC will blow the Oppo away for CD playback.
Marantz SR4001 MPS-1 Cambridge 640C Mapletree Line 2A SE Selah SSR Emotiva ERD Outlaw LFM-1 EX