By turning the volume to 100% on the Parasound, you are reducing the number of resistors in the path of the signal from the preamp to the amp's input stage.
I wasn't thinking about it, but that is a great point. Less crap the better.
Might be a sonic nugget there, SQ quality wise, with a simple pot bypass.
I've done it a few times with fuse holder replacements. From OK, sound to outstanding sound. Top to bottom improvement, in a fuse holder and fuse replacement. Amps, and speakers both..
Regards