Doing an HT redo...

I think the Marantz processors can be set up to use subs in stereo mode and not use them in Direct and Pure Direct modes. Been a while since I thought about it though.

I really don't care what main channel speakers you end up using in this awesome system you have but I think it would be wise to get rid of the Polks and use Ushers as mains so the Center channel matches. I think you kinda hinted at that with the comment that the Ushers out perform the polks but a lot.
Either way you end up for this system, Run ALL speakers in small and let the SVS sub's do ALL of the low end extension. You can move around the subs to get even proper bass in the room, you can't however do that with any of the channels ground level.
What most people get hooked on me included many years ago is the fact that if a speaker can play down to a certain frequency that I need to do that or I wasted my money buying speakers that can do so. What gets really missed here is how bass reacts in the room.
Everything above lets be honest 100-150hz needs to play out of the ground level channels. The sub however need to be crossed over at 120hz for 2 reasons. 1- to play the entire LFE soundtrack of movies. LFE starts at 120hz. 2- Bass management is better suited for subwoofers properly placed in the room and tweaked to perfection.
Your amps will now have more dynamic range as they will not have to send speaker level signals to your ground level speakers . 80hz usually is a nice point of crossover for all channels due to the slope of the point and the in room response. Just about all of the time all kinds of different kinds of speakers sound much cleaner fuller and rich with the removal of low end. Especially when they are integrated perfectly with the subwoofers in the room and you my friend have a nice pair there (LOL).