when to down sample

i have just hooked up a new onkyo dv-sp302 to my older hk 20ii using auido reacerch pro cables. down sampleing was pre-set to the on mode. manual says "if your av amp (or other connected componets) is compatible with high sampling rates (96 kHz), set this to off. i am using analog auido output. any suggestions welcome.

also have a ground loop hum from dish network line. which magic box do i need? i've seen them for $7 for direct tv lines. is there something similar for dish net?