A guess. If the Lamm has a highly sensitive input, say on the order of .5 to 1 volt, the ARC probably has a high enuf output to render the volume control near useless - that is, it is way too loud when the volume control isn't even advanced to 8 o'clock when you are using sources with high output, which causes you to loose the use of the finer gradiations on the volume control. Many ARC amps either employ a built in switch to attenuate incoming signals (my SP10 does) or allows for a minor change on the circuit board to obtain the same effect. Check with ARC to see if they have a provision for attenuation.
Too much voltage in a preamp??
An Audiogn member just sold an Audio Research Ref 2 Mk2 preamp here on the site that was only a week old becaus he said it had "too much voltage drive for my Lamm 1.1 amplifiers" What does that mean? When searching for a prospective preamp, how would one know how to avoid an amplifier mismatch like this?