Glad to see people using panning (and yes, I'd say that that is the correct term) with the panpot controls. All too often I see and hear two trumpets, saxes or whatever both centred.
I teach my students this: If you have two solo instruments both panned to the centre, then that's like having one musician standing on top of the other one's shoulders on stage. It doesn't happen in real life (or would be rather comical if it did!) so you pan them, maybe to 10 o'clock and 2 o'clock respectively so the musicians are effectively standing next to each other.
Some sounds, like stereo strings and stereo brass, can be left centred if desired, of course.
You can also try to get some sense of 3D 'depth' of sound but adding just a little more reverb to sounds that you wish to appear further away from the listener. If you're into creating MIDI files, you can add a slight time delay (really awkward to do on the keyboard but easy in a DAW) as well. In order to sound authentic, that time delay must actually be longer than the actual time delay you'd get in real life. I used to have a table of distances and time at one point.
