does that translate to: if the equipment is truly balanced, then the XLR interconnects do not make a difference, but if the equipment isn't balanced but instead just has XLR but is really single-ended, then the XLR cables matter similarly to single-ended cables?
@jji666 No, a lot of gear out there really is balanced. But that isn't the same as saying it supports the standard. To support the standard, AFAIK the source driving the cable ignores ground. So a phono cartridge, which is floating, is a good example as is a dynamic microphone.
When it was done with tube equipment in the old days a line transformer was used. To do it solid state you have to have a circuit that is OK not referencing ground (these days there are chips like this one for that) or you use a transformer. There is a third technique using a patented circuit that involves a Circlotron output.
So most balanced gear for home stereo use simply references ground, IOW there are two single-ended outputs, one out of phase with the other. This does not support the balanced line standard, so the cables will affect the 'sound' and different cables will sound different. I think this is really bad because first, the balanced line system is supposed to get rid of this problem and second because if you think about it, none of the cables you ever choose would really be 'right'- we all know that next year the people that made the 'best' in a shoot out would have a better cable (likely for more money) and if they don't someone else will; hence all the answers to this thread with different suggestions!
When your gear supports the standard there's none of that- its all plug and play with no worries and the best sound of the cable possible.