While I can report that I did have full success using
as you put it "a plain old audio cassette player".
Within reason, any suitable player can be made to work
if you operate the MOTOR signal manually which is the
main advantage a genuine Atari deck will give you.
"Right" hook ups was a couple of wires, one grounding
both systems together and the other was a jumper from
speaker out on the player to SIO audio, pin 11 J1.
For playback only then, not easy, but still doable.
I never did much tape creation however, it was mostly
reading prerecorded tapes. And long after posting, the
testing of this file.http://atariage.com/...n/#entry1565431