I had a few minutes to mess with the recorder functions, which I had previously only briefly tried.
I set up my HX Stomp to send CC#1 for RECORD and CC#2 for PLAY.
Configured thusly, when I press FS1 (CC#1) the recording starts. Press it again and recording stops but the transport continues to run.
Recording resumes from wherever the transport is at when I press FS1 again.
Pressing FS2 (CC#2) stops both the RECORD function and the transport, and returns to Zero.
Pressing FS2 again begins Playback.
It works the same with both Toggling and Non-Toggling CCs, which indicates that it ignores the CC Values.
I reset the HXS and AT5 to use CC#15 for RECORD, still works fine.
I also had another go with the Looper, which seems to have been fixed in the latest update (which could be why they're ignoring me).
Are you on the latest version (5.0.2) of AT5?
The only thing I can't figure at this point is the purpose of the REWIND function. You can't (as far as I can tell) stop the transport at a specific point in the recording, so REWIND seems superfluous.