I have tried upgrading a working 10.5.5 MacBook? to 10.5.6, and it had no problems with SD or HD recordings. The remote access thing will be a pain (playback needs the windowing system, which is a pain over the InterNet?).
A) Could you provide the output (from a terminal) of:
MythFrontend.app/Contents/MacOS/MythFrontend -v playback
when playing back a crashing recording?
B) I am assuming the crash happens instantly? (i.e. nothing ever plays). If so , could you provide a few megabytes of a problem recording so I can test it? e.g. email me the output of:
dd if=1066_20090127130000.nuv of=cut.nuv bs=2048 count=1024