I've run into a snag with ADTPro. Using the audio out from my PC, I was able to successfully bootstrap the IIe and load the ADTPro client. But to actually transfer any disk images with ADTPro, it requires two-way communication using the PC's headphone out and microphone in, and I can't get that to work.
The input level on the PC's mic input seems too low for the ADTPro server to hear it. I know it's connected OK, because I can hear it beeping when I enable "listen" mode on the PC and play it through the PC speakers, but it's a fairly quiet beeping that shows as 0 out of 10 in the level meter in the sound recording control panel. This seems to be a common problem, and the ADT instructions recommend using Mic Boost or similar OS settings to fix it. But I've set the input level to 100% and I still get no joy. The PC identifies the input as "line in" as opposed to "microphone", so maybe that's part of the problem.
I have a bunch of different computers in the house, but amazingly only one of them has a sound input jack. Unless I can think of some other way to boost the input signal, it looks like ADTPro audio transfers won't be possible for the IIe. The IIe doesn't have a serial card either, so it might be totally out of luck.
That brings me back to using the IIgs with ADTPro, so I can make disks for both the IIgs and the IIe. The IIgs doesn't have audio in, so the only option there is a serial cable. I have the parts needed to build a custom DB-9 to Mini-DIN-8 serial cable, but I've been putting it off, because it would require reusing my USB-to-DB9 adapter and dismantling a custom wiring job I did for the Lisa serial port. And I actually still need the Lisa serial connection, until I'm completely done testing Floppy Emu with Lisa firmware.
So... there are solutions to all these problems, but none of them seem as easy as I'd first hoped, so I'm going to stop and think it through again. I really would like to get ADTPro working on the IIe, but I don't see any way to do that without building some kind of amplifier for the microphone signal, or finding a way on the PC to boost the input levels further than I've managed to already.