O.K. just got an email direct from HD Headquarters. Now this was an email sent to a friend from the "sound" people and it might make more sense to somebody who understands this stuff, so I'll type it verbatum.....
"It's technically possible to do what he wants (add rear speakers), but there's no actual 'canned' solution.
Inside the radio, the high power amplifier operates in parallel with the front speaker amps. (The radio is the 2-channel classic with the ESS amplifier added). The base radio amp is turned on so that someone could potentially add rear speakers.
There are a few issues with actually adding the rear speakersharness:
-A new harness would need to be developed to take the speaker output from the radio to the added rear speakers.
-Fade control: There would be no fade control (since you are essentially using four front speakers).
-Amp level: The rear speakers would have power output at the base radio level, (unless you added a two channel ESS rear speaker kit.)
If you pop the fairing off you will see two spade terminals wire tied to the harness near each speaker. You will need to run these out to rear speakers with the above caveats."
Any feedback from you guys? I think I actuallly understand it better having re-read it several times in order to type it word for word. It's coming to me s-l-o-w-l-y! lol