Yes, that is exactly what these files contain...Audio.
As I don't have a disk setup for my Sol-20 (although I am looking, hint hint) I have to resort to using either serial or the cassette interface to get programs into the Sol's memory.
In this case a .ent file was loaded into the Sol's memory using a serial connection from my Macbook pro, then the contents were [SA]ved back out back to the audio in port on the Mac, and recorded using the program Audacity. I can then reload the audio files back into my Sol-20 by using my old iPod, but it will work direct from a PC, or probably any other audio player that can handle the .wav format, and of course these files can be recorded to a real cassette too.
Presently there are about 40 files I have converted, and I personally have about a 1 in 20 failure rate when reloading back to the Sol from the iPod...not bad.
Phil