Welcome to Bimmerfest -- The #1 Online Community for BMW related information! Please enjoy the discussion forums below and share your experiences with the 200,000 current, new and past BMW owners. The forums are broken out by car model and into other special interest sections such as BMW European Delivery and a special forum to voice your questions to the many BMW dealers on the site to assist our members!
Please follow the links below to help get you started!
The Earthquake SWS-8 subwoofers are drop-in replacements. They fit exactly, right down to the screw holes matching. Very easy. They are available in 4-ohm and 2-ohm versions, so you need to be aware of what you are doing with your amp. I'll expand on this point if you need, just let me know if you are or are not aware of impedance matching between speakers and amp.
The amp is somewhat more complex, mainly because it's not easy to get a line level signal from the OEM BMW head unit to an amp. I selected the Blaupunkt PnP amp because it is designed to work with OEM head units, and you can purchase an accessory cable that literally plugs in to the back of the BMW head unit, intercepts the line-level signal, and delivers it to the amp with a plug properly terminated to interface with the amp. This is highly recommended; much, much simpler than engineering a one-off connection.
Really, if you have the standard audio system, as I did, no upgrades you make will help much unless you upgrade the amp; it is so completely underpowered. In my view, assuming typical speaker sensitivity, you need something like 40 to 60 watts per high-end speaker and no less than 200 watts covering the low end to accurately reproduce music at satisfying volumes. The Blaupunkt PnP 555 (if I recall the model number accurately) has 45 per 4 channels plus 300 watts to the sub at 2 ohms - you could use more but this is enough. The stock amplifier has something silly like 8 watts per channel plus 15 or 20 to the subs.
Hope this helps - please feel free to follow up with more questions.
I've used Custom Sun Control on Hwy 41 near Dobbins AFB for my past 3 cars ( http://www.customsuncontrol.com/indexcustomsun.htm). They tinted my 2007 E90 and after 2+ years I have no scratching on my tint. They are not the cheapest but their work is excellent. I would just make them aware of your concerns about the felt treatment and potential scratching (that it seems to be an issue for some folks). I think they'll know exactly how to deal with it.