New member - trying to sort out tags - any advice please?

I have just moved into Naim-land for the first time and am delighted with my Unitiqute.  I have ripped all my CDs into FLAC using EAC and have them on my PC which has Windows Media Player.  All the folders look fine, showing pictures and using the Album Artist category to list the composer of the piece. (I also list the composer under the Composer category and use the Contributing Artist to show the performers of that particular recording).

For some unaccountable reason the n-stream app shows the performers under both