Processor input

I have a Audioresearch Ref 3 for testing, but no user manual. I'm comparing it against my own preamp and would like to connect it to the processor input of the Ref 3. The thing is that I can't find out how the volume of the processor input is adjusted. Now it seems like it is about at the 2/3 point of the scale, and I see no reason not having it on maximum.
Generally, the gain through the processor input of a preamp is fixed and used as a bypass.

At least it should be, but not on this one and not on my Arcam C30. Anyone with a manual or someone who knows where to find it?
The processor input is fixed at unity gain. This means that the loudness of a surround processor will be identical to what you would hear if you listened to its output directly. That is the whole purpose of a processor input. It is technically not a pass-thru in the sense that you are sending the signal through the active gain stages, just at a fixed attenuated level.

For this reason and a variety of others, I would not use the method you describe to compare the two preamps. The sound of the unit plugged into the REF3's processor input will be affected, sometimes for the good:]
Thank you! This was more information than I asked for, but most certanly apriciated. The posibilety of the REF 3 affecting the signal in the processor mode has crossed my mind too. Actually I have never heard my C30 perform so well before:-).
I can attest to the fact that running a pre through the processor loop does improve the sound of the processor.. I saw the same thing with my LS-26 and Meridian 861.