Rebel: I am not sure if I understood you fully... Did you try the 7.1 channel input and find that it still allowed you to enable DSP modes while in 7.1 channel input?
If this is the case (7.1 channel input DOES allow DSP modes to be activated):
I incorrectly assumed that the 6-channel input would be a way for the receiver to give you Direct Stereo without the "Direct Stereo" mode. On most receivers this would work, but yours apparently is more advanced.
If DSPs can still be activated with 6-channel input, that means that your receiver has analog to digital converters on all channels, and thus is able to do processing on the signal in the digital domain. Since that is the case, then just run it to the CD-R in. I assumed that it would not have ADCs for all channels because most receivers do not (but then again, I've never used a Marantz receiver).
If you tried 7.1-channel input and found that DSP modes CANNOT be enabled then:
I would just use the front two channels of 7.1 input since it is essentially the same as a Direct Stereo circuit because no processing can be done since the receiver doesn't have ADCs on all channels to do digital processing on the analog 7.1 channel input.
