Changing out stereo head unit
"Satellite ready" headuniits typically require the separate purchase of a tuner. Crutchfield.com has excellent information on features and accessories for headunits, though their pricing is usually retail list prices. But, still an excellent source of information on headunits.
Any automotive headunit will fit the opening (and be substantially smaller than the OEM HD headunit), but you will need an installation kit to secure the headunit to the bike and provide a "finished look" on the rider side of the inner fairing. Both BT and HW offer installation kits.
As for which headunit, check out the modules offered by BT and HW for compatible units, and figure out which features are important to you, e.g. brand, flash drive, ipod controller, etc.
Several amp choices: HW, BT, Arc, et al.
The typical automotive amp is too large to fit inside the fairing.
You don't mention your bike's model or year. If you have a police model EG, there are serious wiring issues.
As for speakers, there are hundreds of threads on the subject. Use the "search" function and be prepared to read a lot.
You should have a good understanding of the basics by now. As for specific brands, headunit models, speakers, amps, etc., sound is a highly individualized preference, and, frankly, people (myself included) get tired of posting and reposting the same information. So, the "search" function should be helpful; besides, it gives your something to do while waiting for a response to your thread.
Good luck with your project.




