Dan, you identified the problem for me. I had the radio in TNC PKT mode, looked up in the manual how to take it out of that mode and Chirp promptly populated. It did click my Flex PTT, but as you said, that was momentary with no ill effect. I was already using the cable I got from BlueMax49ers made for the TM-D700 so I was fairly sure it was terminated properly for that radio. I'd even talked by phone with Mark there, who told me about having to use the legacy Chirp for this radio and that's what's working for me.
Okay, very glad you got it working, and glad your cable is intended for the D700 itself. That makes things easier.
I definitely disagree about the recommendation for legacy though - "next" has a ton of fixes for this driver, among others. It might have other bugs, but I'll gladly fix them if you report them as I own this radio and want it to work. Legacy will get no further fixes *and* has known bugs that can cause real problems, so I do not recommend it for anything other than the most dire of circumstances at this point.
--Dan