My plan is to use/buy MC boards. (Current PU is a MM but i have an MC PU that i want to use)
How do i use the mu-metal foils?
Should I reconsider and use MM boards instead and contiunue using my current PU?
You’re best off not using the Mu-metal shield if possible, however, if you go for NA523K boards, it may be necessary. Main issue is that having a mains transformer so close to the boards can create noise as they have a very high amplification and are otherwise unplugged or shielded for best sound.
IIRC the mu-metal shield is stuck to the lid, but Naim can advise you further on this, and whether they can still supply the kit after so many years.