An indication of too much gain is how much you need to turn the volume knob to achieve room filling sound. Say, for example: some here, find their volume too loud, when the volume knob is at the 8 or 9 o`clock position.
Two ways to rectify this. One, send your preamp back to Cary, and have them change the gain of the preamp. The second, cheaper way, is to purchase inline attenuators and insert them at the amp inputs.