I'm after the same advice. I have recently bought a 2000 330d Touring. Great car - rubbish sounds. I've seen quite a bit of advice for the saloon cars but nothing for the tourers.
I went to a local ICE shop - they recommended getting a sub box for the boot - but this isn't a great idea when you have two kids and boot space is at a premium.
Has anyone upgraded the touring speakers or head unit? It would be useful to know if you can get decent sound out of the standard speaker positions or enough improvement from a head unit upgrade. I'm not after system that could rattle eveyone within a half mile radius - just something that will let the music sound as it should (i.e at least some bass you can hear and feel).