https://rs6.eporia.com/company_38/7_OEM_System.pdf
An L6i would be suitable if the whole system was being upgraded and connected through it. But for a subwoofer and amp with bass maximized, I think the Epicenter setup above suits it best. I personally will be running both the L6 and Epicenter in my X5 as soon as I get around to finishing up my sound upgrades.