I recently upgraded my H/K stereo in my '05 330Cic with BSW components. I did the full upgrade (minus the rear mids, which were backordered) plus their ib110 infinite-baffle subwoofer that fits in the stock armrest location.
Considerations for me were that I wanted to keep the factory head unit for stealth and integration, I didn't want to have to modify panels or speakers to make them fit, and for the sub I didn't want to lose any of the already-limited trunk space (with the top down). I'm 42 years old, and I wasn't looking for a competition system or something to share my music with the entire city, but I do listen to a broad variety of music and wanted to be able to listen at decent volume levels with the top down... and be able to feel the bass with the top down, which is a challenge.
Before taking the plunge, I installed a mid-2000s (ie US-made) Rockford Fosgate Punch amplifier, nominally rated at 150W RMS mono but likely putting out over 200W RMS. To that, I connected a Energy prefab (ie factory-tuned) ported 10" enclosed subwoofer that normally rocks my full-sized SUV with less amplification. However, in the Cic I found that all of the bass was absorbed in the trunk, even with the ski-pass completely removed. For me, that ruled out any in-trunk solution.
Fast forward to my BSW install. Note that I am using my RF amp rather than the one that BSW currently supplies - their ib110 originally shipped with an RF amp very similar to mine, so Jason and I thought it was worth trying even though their new amp has slightly more power (I think around 250W RMS). Their kit was easy to install, and it turns out that the ib110 packs more than enough punch for me. I haven't even cranked it yet (still breaking in) but I find that it can pound the back of my seat even with the top down.
The speaker kit was also a pretty simple install, the most time-consuming thing was applying all of the sound deadening to the doors - that likely took me over an hour per door. The rest was pretty easy.
The speakers are much clearer than the H/Ks, particularly with cleanly-recorded music. They can also crank up quite a bit louder with clean recordings than the H/Ks did. For most classic rock, jazz, funk, hip-hop the system sounds great. Where it falls a little short is any music that is poorly-recorded or is "busy" - so for example playing Lady Gaga's "Telephone" that has built-in distortion, they sound is even more congested; Same goes for Katy Perry's "Teenage Dream". The same songs play much better in the Bose system in my wife's Suburban. Billy Joel's "Baby Grand" sounds phenomenal on the new system, though, as good as my fairly pricey home system.
Overall, it was an excellent upgrade. Customer service from Jason and Jeremy was always prompt, personal, and helpful - overall a great experience.
2005 BMW 330Ci M Sport Convertible
1970 Porsche 911 T / 2.7RS-spec