Thanks for the helpful feedback! Yes, I do fret over minutiae before buying something new. Isn't that part of being an audio nut? :)
With the Adcom GTP-500II preamp, the volume knob travels from about 7 o'clock (zero volume) to 5 o'clock (max). Using my Adcom GFA-555II amp, usual listening level is about 9:30 or 10:00, 12:00 is uncomfortably loud, and the drivers on the KEF 104.2's are destroyed by 1:30. (That experiment was performed twice.) So based on the comments received here, perhaps a preamp with a lower output voltage would allow the volume knob to be safely turned up closer to 12:00.
Can anyone recommend any other surround receivers in the $600-$1200 range that might sound especially good as a pre-pro with the Adcom GFA-555II? I would like all of the current surround modes, but I don't need phono or video switching.
Here is a link to the review reporting the 0.76V pre-out voltage for the Outlaw 1070 receiver: http://www.hometheaterhifi.com/volume_12_3/outlaw-1070-receiver-9-2005-part-1.html