ahh..I did the manual setup using those tones. The poster mentioned the "75dB" tones and that confused me. That doesn't allow the gain of the preamp output to be pushed higher though. It just affects the balance between the various preamp channel outputs.

My trouble with the Threshold amp was that even at full pre amp gain on the 990, there wasn't sufficient volume coming out of the Threshold to the magnepan speakers. I don't listen at ear splitting levels either. It simply couldn't drive the threshold properly.

The fact that switching the power amp to an Adcom 555II removed that problem, indicates a possible incompatibility between the 990 and the Threshold in regards to maximum output voltage capability of the 990, and input requirements for full power on the Threshold.

Re: your question on speaker quality by position, The 6 and 7 rear channels don't usually see much bass, so I'd use the smallest speakers/amps there.

Ok..my preamp output gain problem when using a Threshold S500e power amp is solved. I made the connection between the 990 and the s500 with balanced XLR cables instead of the unbalanced, and the gain is now more than enough.

I don't really understand why though. There is a toggle switch on the back of the Threshold for each channel to toggle between balanced and unbalanced. I'm assuming that does something with the input impedence maybe. I'm not sure.

Whatever it does, I can now use the Threshold again..which is my preference. The Adcom 555II actually did a very very nice job driving my magnepans. I could certainly have been very happy keeping it in the system. The Threshold sounds better though which is to be expected since it is a much more substantial piece of iron.

Power output is also quite a bit higher on the threshold. The adcom is 200 at 8 ohm and 325 at 4 ohm...which is what my magnepans are. The Threshold is 250 at 8 ohm and 500 at 4 ohm.

If anyone has a better understanding of the difference between balanced and unbalanced amp connections, it would be helpful to have your input. I'd like to understand why the gain went up using balanced.