Well, I for sure don't have any FACT about the headphone jacks, but when I started my search for mine and reading forums I was lead to believe that the second headphone jack was added shortly after the first release of the Omega! But Monte has a history of a pretty early Omega so at this point I would go with that, at lest it isn't just here say!
Mud, It looks like the headphone jacks don't have anything to do with what software version is in the Omega, and as far as I know it never did.
Now! getting the firmware updated in an older Omega is something I just went through!!! (it didn't happen)
From recent forum gossip!
Anytime a detector goes in for service if there is an update available for it, they update it.
Maybe certain models! but in my case not with the Omega.
My Omega pretty recent became non-functional (broken) I contacted First Texas's service department and obtained a return number for service and specific instruction on packing it, labeling it, and properly making out a problem report of ANY and all problems with the unit. I did all of that and in the problem report I also "Clearly" included a request of them upgrading the software if an upgrade was possible, I did that based on forum gossip that they were NEWER firmware version of the Omega being sold, and they were also forum members claiming theirs were a newer version than mine. I never set any limit of cost in the problem report nor in any other contact with their service department. (I had a clearing house to acquire and set aside $150.00 for the repair)
When I got my Omega back as repaired as it was, it was still version 4. (I just checked it again and its STILL ver 4)
Okay, now I'm speculating! it may be possible that if a certain chip or IC is at fault for the failure and that chip or IC is one that houses the firmware and it gets replaced then the replacement "Chip", "IC", or entire "Circuit Board" would have the newer firmware version?? Which could???? explain why mine was sent it as version 4, got repaired and was returned a version 4, because those chips or IC's didn't get replaced in mine.
Mark