A number of IAA compatible generators are not showing up on the "In" list; SampleTank and Alchemy Mobile to name two. Also noticed that the list heading is titled "mono sources".

See pic attached

I guess that the "Mono Sources" refers to the Headset Mic entry. The heading "Inter-App Audio generators" is at the same level as the "Mono Sources" heading, I guess they are separate lists in the same menu.

From the screenshot, it doesn't look to me as IAA was mono only.

Ah. Okay, that clears up the mono sources issue. Still don't know why all my IAA sources aren't listed.