bcrowell wrote ...
Hi, Richard. Well, once recently I tried "Y"'ing up the
tape output of my phono preamp so as to make it feed
two supposedly high-impedance devices, and when I
"A-B"'d the arrangement I could hear noticeable signal
degradation.

There are single-case examples all over the map because
there are no hard standards for consumer equipment. OTOH,
I believe you have a better than even chance that a modern,
low-impedance source can drive several high-impedance
loads without significant side-effects.

For your "once" I can cite scores of times I have done the
same thing without any problems. But you make a good
point that you can't rely on it.