I use those free testing music files (mentioned above) to test PST music data file playback on USB keys and on different Disk format - DVD+/-RW, DVD+/-R.
The USB keys I tested range from old 1G/2G thumb drives I got from the trade show long time ago, to the most recent Kingston 16G/32G/64G. Especially, the 32G was bought just for PST testing. All USB keys are in FAT32 (other format, like extFAT, NTFS, PST will not take it.) All these play OK on my PST.
Note that, If a music file cannot be played on USB, it won’t play on DATA disk either.
Usually, I don’t play music data files on my PST. Because the drive mechanism (same as Marantz SA-10) on PST is so good, I actually “going backwards” by burning my music data files on my server to music CD. Sonic performance is very good on my system to my ears. Only downside is that now I have lots of burnt music CD scattered in my study room. 