Hi Michael,
So both times when you have cloned the disk it has run faultlessly for a few weeks and then you start to see this reboot issue?
Given the reboots of the BM5 only occur whilst the BS5 is in standby I guess there must be some housekeeping task that only runs when the system is not being used, or the problem is related to the power saving mode.
First I would try disabling the power saving in the BS5 menu and see if the problem persists.
Next I would try deleting the music files you added most recently to see if the problem stops (in case there are one or more of these files that the BM5 is not managing to process without crashing).
Maybe even try deleting all the music files (but don't do a recovery) to see if the rebooting stops so we can determine whether it is related to these files or due to some other corruption of Windows system files.
Do the crash logs give any indication as to which process / driver etc causes the crash?
Martin.