Help me out... can't figure this out

Hey guys,

I have an old system of Rotel sound processor (rsp-985) and 5-channel amp (rb-985), which functions fine together. Recently, I tried to add a Rotel rb-990 (2-channel amp) to the above HT-system and eventually do a 7.1 when I upgrade my sound processor.

My initially intentions were to use the RB-990 to power the front speakers and 3 of the 5 channels from the RB-985 to power the center and back two speakers and leave the remaining two channels for a future 7.1 system.

What happens is that when I connect the RB-990 to the "front L/R" preouts of the sound processor and turn on the amp, there is a horrible constant loud noise from the engaged front speakers. It was so loud, I thought I blew my speakers out, fortunately they were fine.

When I connected the 2-channel amp to the "surround L/R" preouts from the processor I didn't get this problem.
Also, I switched out the interconnects and still, same problem.

When I ditched the 2-channel amp and connected the processor to the 5-channel amp (the original configuration), it worked fine.

I don't know why I am having this problem, especially since I've connected the 2-channel amp to the existing system in the past with no problems.

I've narrowed the problem to the "front L/R" preouts of the processor and it's compatibility with the 2-channel amp, but independently neither seems to have a problem when I switched the other out.

Any advice would be greatly appreciated.

I don't know?...pretty strange. Maybe the gain adjustments in the prepro are set to high (all the way up)...and it's to high for the new amp, and it's being overloaded?

Just a wild guess? didn't say what kind of noise it was?....maybe you need a cheater plug?

Are you sure this would happen again? Every once in a while something just happens that cant be explained and never happens again. Does the 2 channel amp have gain adjustments in the front heat sinks like my 6 channel Rotel does? Check those if it has them. Maybe a IC wasnt seated properly.
Just a thought, what is the setting of the two front L&R speakers on the processor end if any? Is it "Large" or "Small" ( please consult your manual)? Have you tried configuring the settings from the processor? Is there a "direct" settings (2 mains L&R) only and have you tried those?

As for the amps, you can compare their sensitivity rating for maximum output. It is possible that the 990 have a higher sensitivity (lower input voltage required) and if so, is there a way to limit the output from the processor side?
I will try playing with the "large" and "small" settings and do a direct stereo setting from the processor.

There is no way to change gain settings on the amp.

Thanks for the suggestions!