I just upgraded the standard audio system for my 2015 85D to a custom one designed by SRQ Customs. Ryan of SRQ Customs built a subwoofer enclosure for 2 10 inch subwoofers. The enclosure is designed to be situated in the footwell. The cover is completely removable as is the entire enclosure! If anyone is interested, Ryan is able to build one for your and have it shipped to anywhere in the U.S. By the way, the sound quality of my custom build is out of this world! My new system sounds even better than the Ultra High Fidelity, which I had in my 2012 Tesla Model S (recently sold).