The different between G-9000 and G-7000 is the wattage.

G-9000 is 160W per channel

G-7000 is 85W per channel

The Pioneer SX-850 is 65W per channel but compared with the Sansui receivers you are looking at, it is nothing.
If you get the Sansui receivers you are looking at, you will be very happy and they have a lot of power. There is a G-9000DB. Those receivers cost a lot and they are hard to find!