I have this preamp, well the CS-115 which is the same one without tone controls, and it's a very serviceable preamp in active mode. A little hifi sounding, somewhat lacking in nuance. However look at that direct/bypass button, it switches the unit to passive mode, no active circuits in the signal path, and this transforms the unit to another class. Lush, beautiful sound, deeply layered soundstage with finely drawn images. Of course you lose all gain so the source components have to be up to driving the power amp and the dynamics vary accordingly.
Did you get the optional phono board with yours? Also I believe balanced outputs were also optional on both preamps. These two pre's were the lower priced option to the Pro 5 and Pro 10 in the line, but all of the early B&K preamps were afterthoughts to the blockbuster ST-140 and later and greater ST-202 power amps that Van Alstine claims were his design. I'll stay out of that argument and only note that many feel all B&K components were somewhat less than spectacular after those two amps. They soon switched their focus to home theater and went out of business a couple years ago.
(Not to be a nebbish, but should this thread be in the Solid State circle?)