The set top box is not too "technical" for the TV - it spits out audio and video in the exact same way the DVD player does. If the DVD player is working, then the set top box should do the same.
Easiest way to do this is to eliminate the DVD player and switch - just hook the set top box up to the back of the TV, change the TV to the AV channel, and turn on the set top box. I would assume that even if it's not receiving anything, it has menus and so forth - bring up a menu and you *should* see it on the TV screen. If you don't see it on the screen, then double check your cabling, and double check the set top box. Check the instructions to make sure that you don't have to manually select an output mode on your set top box, i.e co-ax, AV or HDMI being your options from what I see in the photos.It *should*output on all three, but I have seen devices where you have to manually select, so it may be worth a shot. Until you get to that stage, none of us can really help...

