Son, another welcome. First, about your location in the room. If you could be in the center, that would be better, but as long as you leave more than about a foot of distance between the outside M60 and the side wall, that should be okay. Since you're working with the 13' dimension, I assume that you'll be sitting very close to the back wall, so a suitable location for the QSs would be about 6' up on the back wall and widely separated, since they're side surrounds, despite being mounted on the back wall.
As to the exact speaker complement, keep in mind the 10% and 5% discounts which Randy mentioned, when accommodating your budget. Two specific points I'll make is that you consider a vertical M22 center for wider and smoother horizontal dispersion, if it can fit into your room arrangement and that if possible you fit the EP500 into the budget. I've had one for about four months now and can give it the strongest of recommendations.
