I can give you my 2 cents, if you are using Spektrum your choices are limited. If you want to use a SRXL or single line receiver, you'll have to use the SRXL2. To do that you'll need the 76401 adaptor because the SRXL2 needs to plug into the side of the unit unlike the regular SRXL. There are videos out there on how to do it but it can get confusing. Or you can do the standard receiver setup which will work with any of the new Specktrum receivers. I wouldn't run just one satellite on a 500. Now as far as the 4651T serial receiver, I have never tried that but its the SRXL2 technology so probably need the 76401 also but not 100% on that. Unless you could find a AR7700 left over somewhere, they worked great, but they discontinued them..
T