It is possible but you have to hackit! The .chl files have a header which is 0x418 bytes long. Then follows a variable length channel record for each channel.
To join two chl files:
1) Remove the header record from the second file using a hex editor like HxD.
2) Append the second file to the first file.
3) Byte 0x8, (the ninth byte in the new file), has the number of channels in the file which you can set to 0xFF.
Then import the new .chl file into TotalMedia (I'm using v3.5) to fixup the data and edit channels to remove duplicates.
I kept it as simple as possible. You can break your TotalMedia installation if you are very unlucky and try to import a corrupt .chl file.