It's been a few years now since I posted the original issue on this site.
Since then we've used quite a few 6501's on various systems (nice cheep solution for DIGIO); initially to make them more stable, we removed the power lines from the USB cable and supplied external power.
We looked at this again a few years ago now, as it was still not quite right and we moved to using a USB optical isolator, cheaply available via Amazon and this has sorted all of the hangs.
One word of warning, only put the optical isolator in front of the 6501, it may have an impact on data throughput for other devices.
