Eh for me it's more than the gun sound effects. During the opening in the future, the synths are missing in the 5.1, you only hear the ambiance (specifically the shot of the unnamed solider running). During the part when Kyle and Sarah escape the police station I don't think I could hear the main synths (the sounds that give the scene a sense of urgency) but I gotta double check on that. And during the end of the last chase when Sarah runs over the Terminator, I can't hear the "mechanical noise" as the truck flips over (when Sarah screams). Instead I hear music that I've never noticed before (the loud drums).
That's just off the top of my head. This is one of my top 5 movies ever, and having watched it probably over 700 times (I was born in '84), as well as someone who has an eye and ear for this sorta thing (even as a child I could point out things like bloopers and stuff) I can say for sure that the problems with the 5.1 mix go way beyond simply the new gunshot sound effects.
That being said, I d-loaded this and browsed through it yesterday and I noticed in certain shots that the teal look is still there. Towards the end of the first chase, during the part when Kyle is getting away from the other police car, one shot looked teal then the next shot following it immediately had a natural palette (extinguishing my doubts as to whether this was how it was supposed to look). Thankfully though this video doesn't close halfway through when Sarah finds out her friends are dead.