The Alpine is installed in a Golf single DIN adapter with a cubby hole below the Alpine for sunglasses etc. Audio quality is very good.
i've actually got the Alpine and ipod controller in mine too.
if you want full control and decent quality sound then get an alpine HU with Ai-net and the KCA-420i
you can sort music directly from the HU by playlist, album, artist individual tracks are easy to find as you get the alpine "search" / quick list functionality
only downside i'd say is that cycle through the list using glide touch is bit slow for me, but then i guess you are meant to be watching the road and not your playlists.
if you want to keep it OEM then your other option is to get a double din unit that can take a full speed interface, i know you've got sat nav already but you could easily sell that on.