Hum with VTL's

Using the RCA cables grounds one chassis to the other. Using the balanced evidently does not. Either the balanced sockets are floating on one or both ends or your balanced cables don't have a connection from end to the other for the body of the shells which would ground them. If using the RCA cables grounds everything and that solves the hum then I don't see why you can't do that. If all the equipment has three prong AC plugs then that would also ground them together.

BTW, your equipment draws more current than the P600 is designed to provide.

You have a ground loop. Try to connect everything to a outlet strip then use another outlet once. this fixed my prob.

Herman Thanks for advise.
I've tried different cables and they are the same so it's not them. Does this mean the balanced sockets should all have a grounding to the chassis of each commponent and I have one or more that does not have this connection ? Could this be a design issue or would it be a defect ?
Similarly as all my components have 3 pin mains have I lost earth continuity to mains on a component. If I have a design conflict between components which my bridging with he RCA solves then I can live with that I just don't like the idea of having something that is not right or has a defect !!
On the P600 it normaly shows an output reading of 450-500 Watts as it's supossed to be a 600 watt unit I thought it should be OK ? Mind you it does get a bit warm !
Many Thanks Ade