With this rattling around in my head, I re-read the Z7 manual one more time.
I note with interest:
"Only analog signals are sent to the second, third and fourth (analog ZONE 4 OUT) zones. Any source you want to listen to in these zones must be connected to the analog AUDIO IN jacks of this unit."
Of course, EVERYTING sent to second, third and fourth (analog ZONE 4 OUT) zones is analog BY DEFINITION. So they MUST mean something like analog signals at the analog inputs--and even then, it also sends Tuner, XM, iPod, SB, Net and so forth.
But wait. There's more.
"When this unit is in the party mode (page 129), audio signals input at the HDMI IN jacks or DIGITAL INPUT jacks are output at the ZONE OUT (ZONE 2/ZONE 3) and OPTICAL (ZONE 4) jacks."
So, not party mode == must use analog cables to get sound out for the zones and party mode == doesn't use analog cables to get sound out for the zones even if they are there. I have no idea what that means to my underlying question.