could you tell us some of your steps in digital performer to mix these 4 channels...
Create 4 mono tracks (unless you have 2 stereo files, then you would create 2 stereo tracks), Pan each properly (L, or R 100%), then assign the output of that channel to a stereo subchannel. If I used 4 mics, then each mic would have it's own mono channel, those would go to two stereo subchannels, with the output of those going into a master fader channel. This way you have full control over each mic, and I put cards and omnis on their own sub-channel, so I get to mix those to my liking in the subchannel. With a soundboard, it's the same process, just more tracks.
Wayne
Edit: Maybe this picture will explain it better.... (FYI, in this case another submix is being made, all the mics are being fed into another channel (mics) which is used to blend the amount of mics vs. board in the final outcome).