I took a quick peek at Capture a moment ago. I seem to think if you're recording 4 mics at once, you'll have the option to here ALL tracks back on a L-R playback within Capture...which plays back on outputs 1 & 2. Would this be why you're thinking that you're only hearing Mics 1 & 2? I'm not sure if you use Studio One, but there is a function in the Capture menu under SESSION to export all of your tracks. You could probably then load them into Studio one.
Another thing I'm thinking is that the 3rd and 4th mics could be out of phase (?) cancelling out... please let me know if you've made any progress. I'm interested in hearing!