Hi!
I saw this thread a couple of days ago when doing research whether the new USB interface (the black one) would work with my Variax 500, which is older than the 600. I just wanted to be a good internet citizen and tell you that it does!
I was a bit worried after reading this thread but one review at Thomann said it worked with his 500 so I took a chance. So it must either be your Variax that is faulty or something else.
You said you had tried several laptops with different operating systems. I got it working with Windows 10 64-bit, however it runs in a Virtual Machine using VMWare because I don't want to install Java on the host operating system (also Windows 10). Like you I downloaded the 32-bit version of WB and Java Runtime Environment (you can use a later JRE than the v.6 that WB tells you to install, I used 8) and it worked immediately.
You don't mention if you have tried a different ethernet cable but I don't think that's the problem, but maybe try anyway. Supposedly any cat5 that isn't crosslinked should work but I'm not 100% certain and I don't dare to try myself.
The main reason I got WB is to do drop D digitally to maintain tension and better intonation, but wow it is so weird to play. You hear D from the signal in the speakers but "feel" the vibration from E in your body, even with headphones.
It sounds good though and the intonation is so much better when tuning in E. Intonating the low E tuned down to D was almost impossible. Getting the 12th fret and open string in tune was fine but all the lower frets was awfully out of tune.