Okay I know a number of forum members have had subwoofers installed in their M5 weather it was a custom install or an M-Audio upgrade. I wanted to share my installation outcome that I recently went with. Originally I had a 10" subwoofer box in the trunk and it produced great bass but I wanted something that would take up minimal space, look like a custom installation and produce great sound. Well I came across an install that used the area in the right side of the trunk. I sent my trunk trim piece to a company in Sarasota Florida called SRQ Custom Autosound, Car Audio in Sarasota Florida – SRQ Custom Autosound and they made a custom 1.0 cubic foot sub enclosure to fit the inner side well of my trunk. Through further conversation with SRQ I elected to install a 10" Hertz Energy Subwoofer in the custom enclosure. It took SRQ two days to build the enclosure, install the woofer and ship it back to me. Upon installation in my BMW all I can say is "AMAZING". It sounds so much better than my previous set up and I have all my useable trunk space. I am very impressed with the sound quality, craftsmanship in the building of the sub enclosure, and attention to details that SRQ exhibited throughout the build of the final product. I could go on but I let the pictures speak for themself.