It is a Trisync crt monitor right? Not just a regular crt?
I'm not sure about the new drivers or the Trisync but with my old 15k arcade monitor, you could only use it by itself with the AVGA. It can't output the 2 different signals to the 2 outputs at the same time. (Maybe this changed?) Or maybe you can with the Trisync? I don't have one so I'm not sure on that part...
Yes, so long as you have -switchres enabled in the ini (or wherever) MAME should switch to the correct resolution for you.
Also remember, this is all coming from my memories of doing this years ago so I apologize if I'm incorrect on any details!
Enjoy the new monitor! & GL!
Pessimist: Oh, this can't get any worse!
Optimist: Yes, it can!