Hi,
did you try to connect the Tyros using D.I. boxes? Does other sources show the same humming?
Did you try to connect your Tyros with another mixing console?
Is Tyros and the other equipment powered by the same electricity system?
Is it an Tyros made for USA or made for Europe and used with an convcerter?
Or is the mixing console made for USA?
Or does Tyros share the same electricity system with light equipment?
Is the Tyros's electricity cable grounded or not (my 9000 hums when I connect to my HiFi equipment with antenna)?
Or what about USB connection?
I have trouble too, connecting the computer to other grounded equipment.
Is an audio cord parallel with an electricity cable?
There are many reasons possible. I would check with mixing console and Tyros using head phones and no other equipment.

------------------
Regards
RF