The link from the OP for the instructions on how to use FRE:AC with Pinsound is no longer available. Below is the text of the instructions courtesy of the Wayback Machine.
Sound file format
The PinSound board and the PinSound studio can only run properly with WAV sound files! (New versions support OGG apparently too, I still convert)
How to convert sound files to WAV
You have to convert any sound file to WAV 16Bits PCM stereo, simply follow this procedure:
Download fre:ac (free audio converter, for Windows, MacOSX, Linux)
Configure fre:ac to wav encoder
In Encoder section, select SndFile Output Component
Then click on Configure encoder
Select file Format to WAV (Microsoft)
and Audio format to Signed 16 bit PCM
In Output folder section, select Use Input file folder if possible
And still in Output folder select Allow overwriting input file
Now uncompress the ZIP archive to a temporary folder.
Drag and drop the previously uncompressed folder to fre:ac
Hit the green Play button to start converting.
After few minutes, once the conversion is done.
Create (if not present) a folder named audio on the USB flash drive and copy into this folder the previously converted audio mix.
Safely eject the USB flash drive and plug it back to the PinSound board, you are done!
What isn't covered here in the instructions above are few thing I will add here.
I don't know if the newest version of FRE:AC is a problem, I was getting frustrated with the file renaming adding in stuff I didn't want. So I decided to use a previous version more closely dated to when these instructions were written (Aug 2016) I used this link for older versions listed by date.
I would grab them now as you never know when this kind of stuff goes away. ---> https://www.videohelp.com/software/fre-ac/old-versions
Also, The instruction don't tell you to change the renaming so it would correctly write the folders from the source and not "unknown album" crap.
Under "General Settings Setup" change the default "Filename Pattern" to whatever it is showing to just <filename>.
general settings setup (resized).JPG