Further update. I have today installed a powered hub to see if it made any difference (mainly because sorting through my Compter bits I found I already had a Belkin one here). Did it make a difference, it certainly did - it made the problem of Picsender 'hanging' far worse than it was before! Can't really work out why that should be - only perhaps that the stable voltage on the USB hub has had some effect on the possible EMI being generated to be more regular?
Have removed the powered hub now as I see it as a retrograde step at this point. That aside, my Tripp Lite Cable has not yet been delivered so won't be able to to try that until later this week. However, I have ordered a bunch of capacitors, and intend to apply these to the brushed spindle motor, which I think may be the source of the interference. More test test test and assess from there. If no improvement, from that point on, I intend adding caps to the Probe and Limits inputs and see what that does....
Will keep you folks updated with prgress as it goes along.