It's not clear from your post if you moved the speakers from the 3805 Surround back / Zone 2 terminals to the stereo amplifier. If you did, the problem probably is that the Zone 2 L/R pre outs typically only "see" analog connections. This means if you only have digital audio connections between your source components and the 3805 (optical, HDMI, etc.), you'll now have to go back and add analog connections (i.e. the red/white RCA's).
Regards,
Wayne A. Pflughaupt