Yeah, power adders are great. Love my supercharger, even if it drinks premium gas and breaks transmissions.
As for presets, you should be able to tune to a station, long-hold on one of the preset buttons, and then the number on the preset button will change to show the station frequency that it is now set to. I'll check the code to see if anything could be causing a problem, but I'm not aware of any issues.
As for being able to faintly hear the radio, that's an interesting one. The way it works, DriveLine sets the volume of the audio input line to zero when you mute it or change to a different media source. If some volume is somehow 'leaking' in through the audio line, there are changes I can make to the code which should prevent this.
Maps should just work. As long as you're online and your GPS has a signal. When you open the Maps screen, it may take a few seconds to refresh. In order to conserve mobile data/bandwidth, the Maps screen only updates when you're actually on that screen, instead of constantly updating in the background. Is your location displaying correctly on the Weather tile on the Home screen?