Nice setup! Your idea of that digital to analog converter with the toslink with 3.5 adaptor should work. I'm curious on your results on that. For my tablet i'm using an archos 70 but my headunit is stock. It does have Bluetooth a2dp so i use that since there isn't any noticeable distortion surprisingly. I totally agree with you on tethering your phone for internet. Just makes sense since your paying for internet anyway might as well make use of it. I'm assuming that since you say its unactivated that you bought the unit outright correct? just curious so basically you use it via wifi and or cell phone tethering. Also You don't have any pics up of it setup on your windshield yet I'd love to see it.
You still working out the kinks and details on the car audio stuff? From the looks of it should be a real nice sq setup with the image dynamic horn tweeters and foals when you get it done. I have heard alot of good things about image dynamics horns and their idmax subs. I had a pioneer headunit once in an old car of mine they sounded good and have lots of preamps for building nice systems.
Hey as far as EQ is concerned since you have a rooted evo4g if your running a gingerbread rom you might want to check out the Equalizer app from the market. https://market.android.com/details?i...apps.equalizer this way you can have system wide eq for use with whatever music app you want. Just a suggestion or idea to check out. I'm on a stock froyo rom so i can't test it but heard some good tings about it.
Whenever you do get that whole thing sorted out i would love it if you posted it on my site. Just started it (less than a month old) and it's a community like this only for android car enthusiasts like yourself. I have a gallery for android car installs so if you want to show it off feel free. http://www.android-car.com/Show-Off-Your-Ride.html I'm in the Process of getting pics up of my install myself. You can check out some info on what apps and what not I'm running there.