whats the difference?

Mac tells me to plug my 501 mono amps directly into the wall.Richard gray tells me to plug them into my rg 400 pro.I've tried it both ways and don't really hear any difference. Other than surge suppression ( which mac contends isn't necessary in the 501's as they have built in protection), what difference should it make? What should i be listening for?
the effectiveness of these devices has been disputed for some time now. Check this out...

Truthfully if you aren't hearing anything that is a good thing because you don't want the RG 400 to color the signal. If anything, most people hear a lower noise floor or expanded soundstage or increased dynamics.
DO you have a dedicated line?
no- its a 20 amp line in an apt.
I plug all directly to the wall, including the RGP. In my system there is a big difference with and without the RGP.