I was about to post that bypassing the processing and patching the A/D through to the outputs would be the way to do it, but I didn't realize someone had actually done it. Very cool.
csero - did you just patch through to the modulator inputs on the amp board, or did you patch into the processor board somewhere? I want to replicate the front mains to the surround channels without the party-mode delay, and patching the I2S lines would seem to be the easy way. I could do it at the modulator, but I was wondering whether there was easy access to them somewhere prior to that, maybe avoiding noise pickup. (yeah, I know - I should get a service manual).
Of course, I'm using an XR25, so the layout may be completly different.