I think you will discover that Naim have to do the board change because the original board won’t support the new (ie what Naim can get hold of) screens. But I believe the 350 € price or thereabouts will cover both.
The lower price for screen only is basically for later legacy units that already have the board.
I’m also back on the Naim train with a mint NAC112x, NAP150X and ND5XS. The last 2 years 1 had 2x times Nait XS (midbass coloration/channel imbalance), UQ2 (not enough power for Kef Q550), SU (a bit lifeless on analoque inputs) and Nait 5italic (very noisy and a strained sound when pushed harder).
NAC112x, NAP150X and ND5XS+Kef Q550/Rega planar 2/Marantz CD5005 (dig. connected with coax cable to ND5XS) is my first Naim amp/source which has no fatigue midbass coloration and really is dead silent (no noise/buzz what so ever). It simply playes music in a enthousiastic way. So i’m finally happy