Finally I made some progress:
For the dump in my last post I found out, that I was dumping with 16 Bit. Therefore every first and second byte are interchanged.
My second problem was the way I was sending the commands: I was using "echo -e '\x0D\xA1\x00...", but actually it required parameter "-n" as well: "echo -en '\x0D\xA1\x00...' ".
Looks like the PowerMax Pro with my firmware always sends these 0x00 0x58 etc. when idle.
For me it was not necessary to do an enrollment, I could just send the command to arm the PowerMax. It was successfully armed.
Thanks a lot for your support.