I've recently tried using my LS-2 to split the signal between 2 amps and I got hum. It may have been the particular arrangement of amps, cables etc but I don't know as I never bothered getting to the bottom of it. Must try again soon.
I get hum when I split between my Orange TH30 and my Roland, but not when I go between my Roland and my solid-state Vox AC30... I wonder why that is? Surely solid-state circuitry isn't the solution, since they're all powered off the same mains?