You can use the 990 for 5.1. I am confused though that the 990 did not find SL/SR speakers. It should have found these, but not the SBL/SBR (surround back) speakers. If what you staed above is correct, you need to move the SBL/SBR preouts to the SL/SR preouts. The 990 will support 5.1 with no issues whatsoever.
Was typing as you replyed. You are correct in your discovery however.
_________________________
Doug
--------------------
HT Site