The 2900 is essentially the predecessor to the 3910....The 2200 is the predecessor to the 2910, so no it isn't "significantly" better. I've heard all of them and they all sound more similar than not. The 2900 is smoother and has better separation than the 2200 and 2910, but is pretty much indistinguishable from the 3910 to my ears. The 3910 will be an upgrade from the 2910, but it isn't going to be night and day from what he already has.
If he wants better PQ, a high def player would be the way to go, not another upscaling DVD player. (which was his actual question...video not audio) The problem with that is, there isn't a high def player that is universal audio wise.