I've now bought a small HP thin client, a t574. Used on ebay it was 60 with no psu, but I picked up what looks like a very decent psu for a tenner. You can get earlier HP models for 35 or so, but this one has an atom processor so I thought it was worth the extra. Also more memory and flash drive.
Got a 64G micro usb stick for storage, and will now install Slitaz and mpd as people have suggested. Or another one which seems quite interesting is sockso.
However, meanwhile, and as always, one comes on the real solution after having bought an alternative, this seems the perfect solution:
https://store.tinygreenpc.com/tiny-green-pcs/utilite-1.html
This looks really neat. Wish I'd known about it before buying the thin client, which is probably very functional but by comparison very clunky.
The thing that is a bit dismaying is that having started the process of ripping the CDs to FLAC, the free space on the 64G usb stick seems to be shrinking at an alarming rate....
Al