You can only have one gunners position in one vehicle. That's what Evis meant. The 120mm and the coax MG are both fired from the same gunners position. Although not from the same spot on the vehicle.
The AAMG would require the gunner to switch places, which is impossible.
Or use a secondary gunner, which is also impossible.
If you think about it real hard, you'll find out that the only secondary gun (Not missile/rocket weapons) there is on any OFP vehicle is the coax MG.
You can have rockets (FFAR) fire from two separate positions.
But you can't have two MG's fire from separate positions.
Unless you do a workaround like quakergamer did, and use a different class when coding it.
That is IMO not a solution, since it's pretty crappy all in all. (NOTE: I am not raining on your parade quakergamer. I think your HMMWV is excellent, it's just that the work-around for the TOW is not very good. It's the best we can do, but it's still not good)
And yes, you can't fire more than one weapon at a time.
It all has to do with selections and proxies, things which you people unfortunately don't know anything about yet. Evis has been working with O2 for quite a while now, and he knows these things. (Oh, I know them as well...)