Not sure if this is the right place so please move if need be.

I've downloaded a TV episode that's in multiple TS files, which is fine as I can join them using HDTVtoMPEG no problem. The problem is the very first file only has 2 channels of sound where as all the rest have 6 so when I join to one big file for encoding it only has 2 channels as well.

How on earth can I get around this?
Can I edit the first one somehow to show it has 6 channels and then join them all?

Help appreciated.