The first thing to do is to try to figure out what is causing the problem. Before buying other gear it may be worthwhile to try putting a different DVD/VCR/CD player on the cables you are using currently that has been used somewhere without having a hum and see if it is the device. I doubt it is the device, but if it is possible to know for sure it isn't the device that helps to troubleshoot.
I would like to second avoiding Monster Cables. They are severly overpriced. Furthermore
RCA is still an unbalanced signal so it isn't likely that it would prevent the buzz. Something to remember with cables is its fine to have a gold-plated
connector, but signal will always be subject to the weakest link. Not only is the output on must devices aluminium. Furthermore with "gold plated" connectors what is behind the gold probably is the weakest link. I agree with AVGuyAndy that a DI is prehaps a good method to use. Personally I would advise a Whirlwind pcDI. You can Froogle for one, they are about $120. They have a minijack (1/8in) input, as well as
RCA in and
thru on one side, and 2 balanced
XLR outputs on the other side as well as a 20dB pad. That may solve the issue, if that doesn't it is probably that you don't have clean
power. The best think I can think of to test that is to run an extension
cord from another
circuit and run all audio equipment on a different
circuit. The DVD/VCR, board, anything after the board (EQ/Dynamics/
DSP), and anything else that is in the signal flow at that time on a different
circuit. If that solves it then you know it is a
power issue. I guess an easier way would be to unplug unused equipment to see if that makes the hum go away. To do that only have whats necessary to
play the DVD/VHS plugged in. See if there is a hum. If there isn't
plug things in till it appears. When the device is found that causes hum you know that device needs to go on another
circuit. Keep going till you know everything plugged in doesn't cause noise.
Sorry about the lengthy post.