mini2440 for car audio application

I'm trying to get a handle on whether the mini2440 would be a sane choice
for a car audio application (mp3 playing, etc)

(Well, that's not actually quite true.  What I really want to do is build
it into a bicycle-mounted sound system: this imposes some extra UI
constraints, which is why I don't just go and buy an ordinary car head unit
instead)

Is anyone doing anything like this?  My chief concern is the audio output
level: the UDA1341TS datasheet says it goes to 900mV rms (no mention of
output impedance that I can see) and I'm wondering whether this is going to
suffice as a 'line level output' that would be OK to feed into a car power
amp directly, or whether it'll need some kind of "line
driver"/pre-amplification.  I could order one and find out myself, but
thought I'd ask if anyone else has done it already?  

(Oh, go on, have a picture -
http://www.flickr.com/photos/coruskate/387255028/)

Also, if anyone has experience of making the touchscreen rainproof, that'd
be useful information

Hey, that's a cool project you got there. I have some experience in
building automotive entertainment or routing systems. I know that the
characteristics and the absolute maximum ratings are very important. You
need to check if the temperature levels are okay for your application. What
about humidity? You already stated rain. I dont think that the lcd is water
resistant. I wouldnt be so concerned about the audio fact. I think its
always better than what we had years ago, have a try there. Maybe use a
second amplifier (LM386 or alike). Also be careful about shake and crash
values. If you are able to acquire these, not sure if they appear in the
datasheets. On a bike trip the display will be shaken like hell!

Just as a followup, the device turned up a week or two ago and I've been
having a few busy evenings since then.  Haven't tried it with the actual
amp and speakers yet (they're on the other side of town from here) but it
drives my powered PC speakers fine so I see no good reason it shouldn't
work.  The CPU is a bit less powerful than I was expecting, though: I'm
having to find integer/fixed-point decoders for mp3, wma etc as it won't do
floating point fast enough to play them in realtime.

Good point on shake & crash.  Not so worried about temperature as I'm
fairly sure the rider will freeze/boil before the mini2440 does.

You can follow my development progress at http://telent.posterous.com/ -
there's a github link there as well for the code I'm writing

I also have a project to build a car audio player based on Mini2440. As a
starting point, I have been involved with the Rockbox project to port
Rockbox to the Mini2440. The port is not complete, but is usable. Rockbox
is not quite suitable for in car use, I will need to customise the GUI, or
more likely add a remote control unit.

It's rumored that Rockbox may become an application instead of standalone
firmware, this should make it much easier to port to targets like mini2440
which already have a supported OS. I've also thought about writing an app
to run under Linux.

We have been blogging about Rockbox on mini2440 at
http://lyre.sourceforge.net/

Indeed, I've borrowed the WMA decoder from Rockbox :-)