What are you trying to convert them to?
All depend on where you want them to play them or store it.
If you use tsremux and make a TS file,it will play most in any player.
In the other hand,the reasons to convert an HD file to something not HD,defeat the purpose of buying and HD receiver and a HDTV set.
The whole idea about recording HD programs is to be able to store them as is in a hard drive,the receiver will play it back in its original format.
Nowadays,the cheap cost of 1 terabyte hard drive for storage allow you to store big files easily,and preserving the original format,with minimal investment.