I searched but I can't seem to put it all together in my head. I want to keep the stock HK unit (2013) and want to know can I use the PN4.520D with MM651's in the fairing even though the HK is 2 ohms with a set of BT 6X9's ( I think they are 4 ohm) already for the saddle bag lids.

This may sound dumb but with the SS amp I would use RCA jacks into the amp and then how do they connect to the speakers themselves?

Will the 6.5's fit in a RG fairing?

 

you can keep the stock head unit without a problem.

The MM651 speakers will fit perfectly fine (as will just about any other 6.5" speaker) with the appropriate adapter plates available from Dragonfly Cycle Concepts. PM Dragonfly2000 (Kevin) here and he'll provide a 10% discount to forum members.

The impedance level of the head unit is a moot point after adding an amp into your system because then it shifts to the impedance level of the amp that needs to be paid attention to.

You can either use high level inputs for the amp which is your speaker wires coming off the radio (front and rear) or you can convert those speaker wires coming off the radio to RCA jacks, the choice is yours but there's really no reason for the expense on the adapters or the additional wiring needed to use RCA jacks in this setup. Simply use your speaker wires coming off the radio to connect to the high level input plugs for the amp.