Sorry if this has been asked before but I could not find this in a search. I have an Onkyo TX-SR674 AVR. I would like to get an adcom 555 amp. On the back of my AVR I see a pre-out for the sub but thats it. How do I connect the amp to the AVR? Do I need to get a pre-amp and connect the AVR to the pre-amp then to the 555 amp? Thanks for any input.