A couple of follow-up questions.
1) Do you use the Y connector before the 7.1 input or on the 990's left and right rear surround output?
"On the 990's L&R surround output"
2) Do you use a Y connector that is designed to do a mono summing (I have seen some Y connectors that are designed for the old stereo vcr to mono tv type connections)? By contrast most of the Y connectors that I have seen are, if they have any explanation at all, say they are designed to split a signal.
" Mono summing. It has 2 male connectors y'ing down to 1 Male connector"
3) Did you do anything special in the setup? For example, reducing the relative output from each source?
"I used a RadShack meter to check that the combined outputs were in balance with the other surrounds."
Thank you for the feedback. I will have to look through my junk box of old interconnects and cables. I may have one of the old tv cables in a drawer some place.