if TV3+1 works and TV3 doesn't then your system is probably struggling with 1080i (assuming you are using AAC for both, if using AC3 then that is a difference btwn the channels too ie. TV3 = AC3 or AAC, TV3+1 = AAC only)
Ok so where are these AAC / AC3 settings to be adjusted? I have looked in TV server config and MP config and cant seem to find them. The only thing I found was what codecs these things use.