Are you sure it is 60Hz hum? That would tend to indicate you have an issue with pickup of the power transformer's magnetic field (or some other, nearby piece of equipment with a power transformer). Have you experimented with the orientation of the power transformer with respect to the signal carrying components? Have you tried adjusting your wire dress? And just in case it's not 60Hz and is instead 120Hz and higher harmonics - have you tied the two chassis panels together to bring them to the same potential? It would be more likely that you have some sort of ground loop issue with two chassis, and that would show up at 120Hz rather than 60Hz. I'm curious what the motivation was for separating the power supply in the first place. So drastic a mod goes a bit beyond regular tech support for a kit, and it's difficult for us to tell you what's wrong with a layout we didn't design. You are pretty much in the place we would be when making a first stab at a new product design layout. A good place to start might be sniffing out the noise with a scope to verify frequency and magnitude.
