I was looking into this for my 15 SG last summer
Tour Pack Speaker 76000526 $330
Tour Pack Install Kit 76000585 $250
Tour Pack Amp 76000277a $450
Tour Pack speaker Pod 760005050 $250
High output charging 299000028 $490
-------
$1770
Plus installation and boom refresh

I was almost set to do this but the High output charging system just seamed off to me. I wanted to confirm with HD if I really needed that and I could not get a clear answer at the dealer.
Then I had a friend that added a stage II to his Street glide front speakers only and when he did the last boom firm ware update the amp would not work...he lost the Dealer Digital Technician software update and had to go back to the dealer to have it updated again which I guess lets the boom know that there is stage II aftermarket amp installed. The update must have reset the boom back to the default OEM equipment list. Asked the dealer about this and it was like looking into the eyes of a goat. I would not be interested in going back to the dealer after every boom update to get this stereo upgrade turned back on.
With this info I decided to wait...and besides the stereo on our SG really do kick ass. You must really have freaking load pipe and like the speed....or your wife has a really nice quite helmet ...or you guys just love to ROCK it going down the road! LOL.
Not sure if this help...but if you do go with the project...good luck and please let me know how it turns out. I would still like to do if
Cat