NAC 42, due to the DIN connectors, and required external power supply(SNAPS or Hi-Cap), the old Naim preamps are probably more difficult to use with other brands of amps. They don't have their own internal power supply, so you must have the outboard supply(or use a Naim amp).
Also the phono boards are known as "N"(MM) or "S"(MC) and are little cards you can swap out. If the preamp is listed as a NAC42S, then it has the "S" cards.
They would be the obvious choice if you plan to use an older Naim amp, like a NAP 250,160, or 110.
Phono section "S" has high overload margins, and handles low output MC cartridges.
I had a Naim NAC 42S with Hi-Cap supply for about 11 years, along with a Naim amp.
Not bad for SS, but my modded MFA Magus C murders it, IMO.
You know, the whole tubes vs SS thing.