Hi Karl
I sympathise with your plight. Most of our optical manufacturing kit is still being made with serial ports.
We always use Comtrol Rocketports, see here...
http://www.comtrol.com/
We find these to be extremely reliable and are about the only ones that work without any hassle. Might be worth giving them a try.
I have a 'spare' 4 port hub that I can bring to the meet for you to look at. I sadly can't let you have it as it's destined for our lab in a few weeks.
Cheers
Jem
Quote: "There is a theory which states that if ever, for any reason, anyone discovers what exactly the Universe is for and why it is here it will instantly disappear and be replaced by something even more bizarre and inexplicable. There is another that states that this has already happened.”... Douglas Adams 1952 - 2001