And thats you need to know. Some users complained that they use older dacs or other equipment that would "have problem" with low input impedance. While RCA has 10k and, as far as I know, 99% of older devices use single-ended design, they would match perfectly to Pre90 with 10k input.
I agree -- I think this point is getting lost in a lot of the discussions surrounding this preamp. Old tuners and phono stages aren't balanced and should be fine with the 10k single-ended input impedance.