How important is EMI and RFI rejection?


In designing a cable....and what cable manufactuer(s) excell...

Power cords
IC's
Speaker cables
wavetrader
I don't want my to amplify any signals other than the pure music. I wonder if the expensive MIT speaker cables allow RFI & EMI to contaminate the signal from the amplifier to the speakers?
1. Even decent equipment filters the AC line
2. Non-power line induced noise isn’t of a concern in the home environment (no large co-factors like multi-phase motors, baluns, etc).
3. I keep LV and HV cabling separated.
4. I run a fully balanced setup (outside of power at the wall)
5. All my equipment is chassis ground (as it should definitely be)

Simple steps using sound, best engineering, practices.