I was looking into a separate 2 channel tube intergrate amp when a local dealer suggested a separate tube pre-amp such as the Rogue Audio Perseus ($1675) with a bypass HT button. In my case, the front channel interconnects output from the 990 into the pre-amp, then from the pre-amp into the 7500. All my analog outputs would connect to the pre-amp. If I'm listening to 5 channel music or a movie, I would simply press the bypass on the pre-amp which allow the 990 to handle all the processing. You can also retain the pre-amp for the front channels during for 5 channel instead of the 990.

I also considered connecting a pre-amp to the 7500 along with the 990 and use the toggle switch on the 7500 to change inputs. But I noticed there is leakage between the balanced and unbalanced inputs on the 7500. I would have to disconnect one when using the other which I prefer not to do.

I'm hoping my dealer would allow me to try the Perseus at home and try either of the configuration I mentioned above..

Ron