Adcom- audio outs

I have the gfp 555 adcom preamp. I purchased it used without the manual.I would like some help in understanding the two sets of audio outputs to amp: one says "norm" and the other says "lab" I've used both to compare stereo sound but could not notice any difference in sound quality.
It's been some time since I sold my Adcom GFP-555 and GFP-565, but as I recall, the "lab" outputs bypass all of the tone and balance controls, whereas the "normal" outputs have the tone and balance controls in the circuit. If you want the "purest" sound, use the "lab" output.
Go to the Adcom website and download the manual.
Adobe format. Viewer is free at Adobe website if you do not have it. Good Luck.