I created a small gh-page at http://s-a.github.io/sample-db/ which contains an audio player pointing to wav files in a sub folder. Any request on a wave file returns 404. Are there any limitations for hosting files on github.io?
No problem with file size, they are under the 100MB limit (see github documentation)
Your problem come from the fact that github page server is case sensitive.
In your channel.json file, your naming scheme is bpnet_something. But your files are named with the scheme bpNet_something.
Change bpnet to bpNet in file names in your channel.json file, commit, push and listen to the music.