I can't say as I can't A/B test mine. I know pro gear works at a higher signal level than consumer gear, and many pro xlr devices have a switch to set the voltage output range.
As to gear that auto-senses unbalanced connections . . . I guess that would depend on how it handles that situation. It may only be half signal level, since the two legs are usually subtracted on the 3 pin version. The output stage may compensate for this when it realizes there is no load on the - pin. I honestly don't know and it may vary from unit to unit.
I'm curious though. Hopefully someone else will chime in here.
Thats what i'm curious about is signal loss. I would like to use my Denon 3808 LFE out to send signal to a behringer 4000 to power my subs and just not sure on the correct method to hook it up being that the behringer has XLR inputs. Thanks for the input.
I have the same issue going from a Pioneer SC-27 RCA preout to a Artison RCC-600 amplifier. with unbalanced (2 RCA) and a balanced XLR. I spoke with the mfg and the recommendation was to use a Y-adapter on the RCA to the unbalanced 2 RCA jacks. So that's the direction I took!