You can buy a compatible (sp) Sony headunit and speakers of your choice from a discounter, and simply buy the interface module and installation kit from Biketronics. Biketronics makes a great interface module (lifetime guaranty), but charge full retail for headunits IIRC.
Buy directly from Biketronics. Much easier to get help (if you have installation questions) directly from BT than buying from an Ebay vendor.
go with biketronics. chunk the pos hk unit. mine went out with less than 5k on bike and while still under warranty. the sony is much better. if you use an ipod, get the interface that allows you to control (and charge) the ipod from the handlebars. its great.
All i can say is don't get a kenwood. Have one on my 05 that a guy put on before me. shorts out, getting worse, face unt=it doesn't seem to want to click in right I guess. Not loud enough at all and real expensive to get hand controls to work. Really contemplating getting rid of it, it sucks.