Hi Peter:It's interesting how the obvious solution can escape one. I just connected the output of my 570 to the input of my computer's sound card and it works fine. I then connected my headphones to the sound card's output and have the precise setup I was looking for. I can control the audio level from both the radio and the computer. I wondered if I might hear unwanted audio from the transmitter but I'm not.
Thanks to everyone for your help. And Rob, I sent my reply to your note before I'd read Peter's and Herman's notes. It's a bad habit I've always had - to reply to notes as I see them rather than to read all incoming e-mail first. :-)
Cheers & 73s, Steve VE3KC