Preamp inputs - different quality

Bigamp, Are you sure the input trim levels are all set to the same value? Go through the menu to set both level and balance for all inputs you use. Z.

FWIW, Charles Hansen of Ayre believes very strongly in the concept of break-in for input connections. Most of us, I imagine, use one more than others.

This may be a long shot, but is each input individually adjustable for gain? My Levinson preamp has this feature so that all inputs can be adjusted for uniform volume.
If so, it may be that the inferior sounding input simply is set a tad lower in gain, which we preceive as sounding veiled?

is it possible that there may be some oxidation in one of the input ? try cleaning with a tooth pick and cramolin, or the cleaner of your choice and see if the "sound" becomes uniform across all inputs.

Inputs are adjustable and set to the same level. Could be oxidation--I have not cleaned the terminals.