thanks for the helpful replies everyone.
I did have some problems on the digital drive as well - if I ever looked through my cameras viewfinder I would get a little zap off the metal surround - felt like a pin sticking into my eyebrow (I keep the eyecup off so I can cover it when doing darks with that little rubber cover you find on the shoulder strap) This did sometimes upset the digital drive - the guidespeed and TVC would reset to their defaults.
But now with the G11 it is making the 550D not respond to on-camera button pushes (but will still control OK via USB), and I get an error out of PHD, and strange chopped up images from the QHY5.
Marc - that sounds like a good idea changing the USB-serial to go through the hub - actually very obvious - although it had't occurred to me
. I do have a spare port on the hub.
those little poUSB things for $39 euros each might be the go...
cheers
Adam