Thanks Hans. I prefer the flexibility of Windows - don't fancy trying to remember Linux commands in the heat of the moment in a 3am outage!
I might try a fanless PC. We're running both TX's on 10 year old HP i5 laptops at the moment. Nice low loads, but still nagging sound card speed alarms which still occur when I swap from the USB to internal motehrboard soundcard. Therefore by process of elimination I'm thinking it's either internet, or the PC hardware itself causing that.
Unless I'm imagining it, selecting "Synchronise input to output sound cards" to "On" has helped a lot, and increasing "relative adjust" to 1.5%. Not sure how far is wise to push that setting though?
Between studio, and both TX's there are three different ISP's involved, so it's only reasonable to expect and adjust for some jitter?
Please check on which end (and about which end!) those sound card speed warnings are. If "Synchronize" helps, it's most likely the input of Stereo Tool that's wrong. Good sound cards typically have an offset of at most a few Hz ar 192000 Hz. This warning only pops up if it's more than 200!! Hz off, which is really a lot. (Are you using Virtual Audio Cable? If so, try downloading the latest version if you don't already have that one).