IM not really sure if anyone is still viewing this thread, but I have a few suggestions.
Firstly, the need for a DLNA based router and HDD, might really be unnecessary. It depends on your situation though. If you life in an area with shotty cell coverage, or if you are stuck on a data plan that doesn't offer you very much bandwidth, then you might not be able to use the following recomendation.
Look into a server/client app named Plex. This program started life as a branch of XBMC. The major difference between the two is that Plex has a dedicated program for Library management and file serving. What the hell does that mean you ask, or why is it relevent here. Well you set the server up on a home PC, Mac, Win, and Linux are all available. Point the server at your media locations, Music/TV/Movies, it will then go to work downloading meta-data on all of the files, with surprising accuracy so long as the file names are in clean order. For an example, the structure I use which has yet to fail me is as follows. "2001.A.Space.Odyssey[720p].mp4"
Once you set the library up all you need to do is add media to the folders and Plex will automatically add them to the library, downloading cover art, media info such as date, directors, cast, ect.
Now the really cool part. Sign up for a MyPlex account which is free at my.plexapp.com. Sign into your myplex account in your Plex Media Server and also sign into your myplex account in the Client app available in the Google Playstore http://goo.gl/FVqFC .
Once its done all of your media will be available to you on the go. Even better Plex uses HLS (http live streaming), this is the same streaming model apple uses for AirPlay. The advantage to it over something like Flash is that some of the codecs/containers do not need to transcoded, such as MP4. If it does need to be transcoded for playback or if the available bandwidth is too low for a live stream, Plex auto detects this and does it for you. Better still the transcode bitrate of HLS is completely adjustable on the fly, this means if you enter into an area of weaker cell coverage, your video does not buffer and stall, instead it dynamically lowers the quality (audio first, then video). When the signal strength picks back up HLS dynamically raises the quality.
Want to share your movie collection with others, thats cool just have them sign up for a myplex account and quickly give their account access to your server right from the myplex website. This also means that you might not acutally need to worry about hosting the server yourself as mentioned above, if you have a friend with a better collection willing to run it on their system.
I use this all the time in my car and it is always impressive in terms of video quality and responsiveness.
If you dont want to have a dedicated server running all the time back home and dont have a friend willing to either there is another alternative also available in the Playstore. Go check out Navi-X. This thing is FILLED with free Movies and TV, it is a scraper program for things such as IceVideo and the like. Its not quite as stable as Plex, but its free so you cant complain too much. http://goo.gl/fQpiM
If Music is more important to you, I HIGHLY suggest Subsonic. This again is a server/client setup that works much the same as Plex, but is better suited for music. Again you can share you music with other friends as well. YOu can even deligate which of them has access to creating playlists that are viewable to all the users, plus a crazy amount of other cool sharing features.
Subsonic server - http://goo.gl/k8nz
Subsonic app - http://goo.gl/GLoFq
Dsub app (a slightly nicer looking/performing app) - http://goo.gl/xxnB6
Now the last suggestion. The Jellybean interface is nice, but its still not really suited for a car infotainment system. You really need to try and create something along the lines of a 10foot interface. Big buttons and the like.
Here is one I build for my Galaxy Nexus. Ill attach the PSD file so you can edit it according to the size of your screen, though using an app like image2wallpaper or multipicture livewallpaper if you want to have a slightly different image on each screen, would likely allow you to use it as is. After the wallpaper is applied use Desktop Visualizer to create transparent widgets over the buttons baked into the wallpaper itself and set each one to launch the appropriate app.
You will need to download a 3rd party launcher to set this up correctly. I personally run this setup in ADW-Ex http://goo.gl/Z4W9x , though Apex Launcher or Nova Launcher will likely serve you just as well.
The important part is that you need to be able to set a custom number of rows and columns. For this setup you need to set the rows to 5 and the columns to what ever you like. I think I am using 10.
I also have the notification bar hidden, along with the icon dock. I setup gestures to access these features.
Swipe up - opens the app drawer
Swipe down - opens the notification pulldown.
You can use UCCW to create the widgets I have to the left of the BMW logo.
One I made for my buddy with a VW
Here is the PSD should you want to alter it.
BMW - https://www.dropbox.com/s/1ts1gv7uqgr9gp1/BMW.psd
PS - For anyone that does not have access to Photoshop, you can always use GIMP or an even easier alternative is to visit http://pixlr.com/editor/. This browser based photo editor is surprisingly powerful and robust. It will open PSD files without many issues.
HERE IS THE LINK TO THE DROPBOX FOLDER CONTAINING ALL NEEDED FILES!