@TheRealZap
Everything between the HD500X and the Variax 600 is communicating OK.
The HD500X shows correctly when I'm changing presets on my Variax.
But, Workbench 1.75 just says "No connection or no device" and does not react to what I do on the Variax.
When I refresh the Workbench window to the right, it scans, beeps and says "no connection".
So, it seems that I'm stuck with the presets I have on the Variax 600 until Line6 fixes Workbench.
I sure did not see this problem coming when I happily updated from my XTLive to the HD500X.