Why not just do some IR routing or use some of the RS232 outputs so you can use the same codeset with each changer?

I want to say that I did a mx900 with one of those megachangers a couple months ago and had some problems if the dvd player was set to any code set other than 1. I didn't look too much into it as there was only one in the simple theater so I just kept it on code1.