Metal conduit tubing IMO is ridiculous, use plastic. The ground
wiring of the audio cables is all that's needed for shielding.
The mains don't need shielding. Audio and video need shielding
by the cables, but also not by the conduit.
If you really care very, very much about troubles, get rid of SMPS and
use toroidal transformer instead.
2 Cents,
Ralf