In the sample I found on the Internet, it seems like the RIFF format acts as a "wrapper" for this file.
In that case, the first 4 bytes of the file contain the 4 characters "RIFF".
As a codec such as ATRAC may be wrapped in more than one "wrapper", you can examine the first few bytes of your .bin files. Normally for multimedia files, these bytes identify the file's format.
I have managed to convert the ATRAC sample file I found to .wav. The utilities I used were:
Sony ATRAC3 Audio Codec 0.98
WavePad Sound Editor
I changed the file to .oma for it to work, then used WavePad's SaveAs.
However, you will need to do the files one by one, as the batch convert option is in the commercial version of WavePad.
Unfortunately, my first choice of Audacity did not work.