I have found that isolating them from vibration etc is helpful, a seperate shelf would be good but not essential. I have my transport and DAC sitting on top of a roller bearing platform which is itself sitting on my Star Sound rack. They are seperated by a set of Ceraball isolation devices with a VPI Magic Brick sitting on top of them. Probably overkill but sounds good. I have found that most componets sound better with a weight on them, does not have to be exotic or expensive.
