The reasons for rejecting Samba and NFS were mainly around how much time and effort I am willing to invest in getting something working. There's a router doing NAT between the two boxes (don't ask), and I've not managed to get an NFS mount to happen through this connection.
I've had lots of success using Samba from my server, when using it with my WinXP laptop. That's been the primary way of playing music so far. Using smbclient, I've been able to get FTP style access to copy individual files, but I wasn't aware that you could mount external smb volumes on a Linux system. If this is possible, please let me know how to do it, and what the fstab entry looks like.
I'll look into Firefly, that sounds cool.
I know I could make my app do more than pick 10 random tracks - this is just a start.