I agree with Syntax. Koetsu's are extremely sensitive to set-up. My suspicion would be azimuth.
I suspect that very few cartridges, even Koetsu's, have MC motors fixed into the bodies at a precision exceeding 1 degree of arc. After many hours of play and fiddling, I made my latest correction: about 8 minutes of arc, and the Koetsu just SNAPPED into focus. It's a bit of a trial to get there, but worth it. For completeness, I use VTA slightly tail down and 2.1 g of tracking pressure.
Also, consider those loading resistors. Each brand and each type of resistor has its own sonic signature. To the amazement of an IEEE bible thumper, I demonstrated sounds ranging from sublime to unlistenable just by changing one (expensive) gain resistor in the preamp (the most expensive was worst). I like Nude Vishays in my system, but you might also consider Mills wire-wound resistors if sibilance remains troublesome.
About "demagnetizing" your KRSP, I would definitely avoid any active device to avoid overdriving the motor. I use the "demagnetizing" tracks on the Analogue Productions test record, specifically, bands 2 and 3 of side 2.
Good luck, and hope that helps.
