So it looks like a USB stick is feasible, but the OP may have to edit the playlists.
128 gigs sounds small. I thought Naim had advised up to 1TB in the past.
And as I noted, the current version of the software has a bug which breaks this feature. There are a couple of threads. One says that Naim promises a quick fix.
The OP should also be aware that other than playlists, the music is only accessible via the folder structure on the USB stick. In my case, I almost always select my music by drilling down from genre to album artist to album, so my folder structure reflects this. Moreover the tracks within the albums will be listed in alphanumeric order based on the file names for the tracks, not necessarily the track order on the album itself. That’s OK if the file names are. e g. 01 Back in the USSR, 02 Dear Prudence, 03 Glass Onion, etc. which is often, but not always the case.