These ARE NOT .wav files. .chk files are fragments of corrupted data. It is not likely that the homegrown utility we have used here will work since it is not a headerless .wav file.
I would try a couple of things but as noted above clone/image the card first. so you have a backup image of the whole thing.
Then working with the card I would personally try an NTFS/FAT disk recovery solution. Your goal here is to restore the data to your card first. Simple free tools I have has success with include, but are certainly not limited to, Recuva. Man, that program alone saved my ass as the estate archivist about 8 or 9 years ago. I am also a HUGE fan of Stellar Phoenix NTFS/FAT tools, not cheap but also found files deleted 6 months prior.
You can find some tools online that will take the bits of corrupted data (.chk's) and turn it back into a common file type like .jpeg, etc. UnChk is one that is pretty commonly used. It helps to have the entire FOUND.000 folder, intact.
Good luck!