BNC input on 2000 MY 72

I am having problems getting my phono stage to work with 323 boards. The manual says this input is configured for high input and is also referred to as (AUX). See a dealer(very useful!).

Since there are no blacking boards (526 or 326(if they exist?)) so do I need to cut the tracks like on input 5 & 6 of a 52? This would seem to be the only way to ensure the line level tracks are disabled and to ensure the signal is routed via the 323 boards.

Any help usefully received