Considering that basically all surround receivers can create a simulated 5.1 surround from 2.0 (whether it be Pro Logic, Pro Logic II, or one of the receiver's other custom simulations), what you are doing is really pointless and a waste of space as has been pointed out.
Basically all that you are doing is creating the simulation on your computer instead of in your receiver, the end result is essentially the same - a simulated surround track created from 2 channels of audio. You're only wasting your time and space on the disc by doing the conversion on your computer and creating the additional audio channels that would otherwise be processed by your receiver from the original 2 audio channels on the fly. While you could fine tune the simulation if the conversion is done on the computer, most newer receivers do a great job of simulating surround sound. Again, this is basically a waste of time, sorry to say.