Steel works great for RFI noise. However magnetic fields of low frequency will still penetrate the chassis.
Mu-metal is needed to protect from the common source of low frequency magnetic field noise from AC power transformers.
Good news is magnetic fields are very local so separating a power amp (with a large transformer) from other components is usually enough.
Before going to great lengths to modify gear
1) Buy well designed gear to begin with and you won’t need band-aids
2) Use XLR as RCA are woefully inadequate when it comes to protection from RF, ground loops and magnetic field induced hum.
3) A good XLR cable is Canare L-4E6S
Mu-metal is needed to protect from the common source of low frequency magnetic field noise from AC power transformers.
Good news is magnetic fields are very local so separating a power amp (with a large transformer) from other components is usually enough.
Before going to great lengths to modify gear
1) Buy well designed gear to begin with and you won’t need band-aids
2) Use XLR as RCA are woefully inadequate when it comes to protection from RF, ground loops and magnetic field induced hum.
3) A good XLR cable is Canare L-4E6S