I think that pd's midi out doesn't take whole sysex messages though,
you simply send a stream of bytes. This is how it has been working
for me. I created an abstraction which takes a list of bytes and
makes it into a sysex message (stream of bytes) [adds the sysex start
and start and then outputs bytes one by one] and it works quite well
for me.
If it's your list2sysex abstraction then I have already witnessed and tried it...! So far with not more success than using a comma-separated list.
Btw, the sysex loopback code [using the software through] that you
sent initially does work for me.. I get the whole message.