While they don't appear to have published output impedance specs anywhere, I'd be very surprised if it was "high impedance". I'd hazard a guess that it's probably around the 700Ω value that you once posted for the M13. While that value might be higher than on the XLRs, it should've have an issue driving a cable run of any "reasonable" length. Relative to running XLR, I think the greater concern would be noise rejection than signal degradation.
But that's just my opinion: I could be wrong.