Any DSP box with analog already inside is a "you are what you is" Frank Zappa scenerio. Do avoid pure analog processors next to DSP switching power gear. That includes line level EQ's, compressors, mic preamps, etc. I place all my DSP reverbs in their own rack, the analog gear is in it's own rack. I avoid placing anything with a digital clock near any analog gear.
I do use metal racks as they have the best screening and mechanical mounts. I do use isolation washers on each rack screw. Electrical isolation is maintained this way. To check I use a meter to each chassis to ensure isolation.
The reason for that is the "doesn't play well with others" problems you eventually come across. Some gear connects their audio grounds to chassis, some float it, some use a RC network. Without knowing how to read schematics I don't know how anyone can suss all that out and get each piece grounded correctly. That's probably why large well funded installs pay for professional help. The end result should be zero hum anywhere and very low hiss levels.