Benefit of shielded ac wire? Any downside?

THe benefits:
Better rejection of EMI/RFI signals, like from routers, switches etc.
Negatives:
None really, though some claim the sound is duller.  I say it's because you are hearing less noise.

@cleeds . It is standard wire. I just braided it myself. It is a double run, normal wire for in wall use twisted in starquad. Pitch twist about 4 inch. It took a while for 15m. A good foundation for my system. Direct connection to my star wired distribution block, skipping wall outlets & power connectors.  

@ptss:
Run a 10/awg BX- cable solid core conductor from the breaker panel to a metal receptacle box. The metal sheathing on the BX-cable absorbs the (EF)) electric fields emitted by the wires and shunts it to ground. Now from panel to plug is shielded. The upside is low line noise and reduced antenna effect. Downside BX-cable is pricier. Hope that helps. Mike.  

Checking into BX it seems like the sensible option as it also protects from nails, screws and rodents.
I wonder what hi-fi companies that sell high end like Spectral, Pass, Levinson, Goldmund, FM Acoustics, Constellation - advise their clients re home wiring?

Considering that the line/neutral in BX cable is twisted which results in lower inductance versus ROMEX which is separated and parallel, I would like to hear the reasons why BX would result in mushed dynamics?

Lower inductance would make for dirtier transients, but with people pushing low inductance power cords, you need to decide if you are going to have your cake or eat it with that argument.