I have 2 receivers, a 501 and an upgraded 4900. I have Dish 500 with the AT 150 or 180, whatever they call it now.
I was using the 4900 when I got the 501. Since I have only one outlet, I put the 4900 away to use as a back-up if the 501 went out. I still pay the extra receiver fee on the 4900...