Some linear power supplies have optional steel cases, like this R3 Technology case on my 861V4:

[Linked Image from i270.photobucket.com]

I wouldn't have thought this matters too much, as the mains frequency is so low. I did worry that the analogue audio might have a bit of hum on it - not something that Meridian would have had to design out, but there was never any suggestion of this.

I'd have thought that shielding a linear PSU was less important that shielding the DSP boards from everything else.

Some of my LPS modifications have rubber grommet mountings for either the transformer or the chassis, though I'm not sure this is necessary either. Without a spacer to by-pass the bush, the mounting nut can't be very tight, and will need a lock-nut or thread-lock to stop it coming loose.

Nick