I got .IDX och .SON in a archive and .DAT and .XML in Another....
He's sent you a Recording.
A recording should be a folder containing for example:
A folder called R00102
A file called R00102.DAT
The R00102 folder will contain .SON and .IDX files:
B001.SON, B001.IDX
B002.SON, B002.IDX
. . . etc
The FOLDER and the .DAT file must be matching names.
I believe the .XML is created after Hummview has opened and process this data.
Hopefully he has archived the top-level folder:
Folder <--- Archive and send this folder
R00101 folder
R00101.DAT
R00101.XML
Thus expanding & recreating the file-structure is a little easier.