Sure you can do that, but why send the output of PGM 1 to another input channel? For additional EQ or effects? Typically one would submix the 4 channels to a group, and then just monitor from there or send to your recorder or whatever…this is especially common in live FOH applications where the purpose of the submix is to have single fader (or dual fader for a stereo submix) control over a category of sources…like the drums, or backing vocals, that sort of thing, so you can easily pull back or push forward that category in the mix without having to grab a bunch of faders. And then the submix groups mix down to the stereo or 2-buss main mix. So what is the reason for the submix of the 4 channels?