If the polarity switch is on the rear panel next to the IEC input for the AC cord, then I might imagine it is for input AC polarity. However, it is also true that the balanced circuit in at least many of the K&K phono stages permits switching the polarity of the audio signal. Like you, I would expect the switch for audio signal polarity to be on the front panel for easy access.
K&K Phono Preamp questions.
On the front of this unit there is a polarity + mute and - knob. Is the polarity + and - in regards to the xlr outputs? Also on the back panel, there is a switch near the xlr pin 1 ground label. Is this a ground lift switch? Any and all help and other pointers regarding this unit are more than welcome. Thank you.