Pass X-series preamps: shielded or unshielded pc's

Hello all,
This question is for Pass X-series preamp owners who have experimented with both shielded and unshielded aftermarket power cords to use with them.
Do the X-sries Pass Labs preamps generally sound best sonically with shielded or unshielded power cords?
The reason I wonder this is because the X-series preamps contain lots of electronic devices such as an electronic volume control, digital read-out, etc., and a shielded cord might help keep some artifacts from these from getting into the power supply for the audio circuits, etc.