I previously installed the Bavsound woofers and they are a decent improvement to the sound with the stock amp.
https://www.bavsound.com/BMW-Underse...ofer-Upgrades/
I also just added the match up7BMW amp
https://www.audiotec-fischer.de/en/m...ifiers/up-7bmw
I have spent a fair amount of time tuning the amp and I just realized these woofers are supposedly rated down to 20HZ. I previously hadn't tried any boost on the 25HZ slider but I slowly adjusted the sliders and I am actually shocked at how low these subs play and how good this amp with limitless adjustability is!!
I am very pleased with the system and as I get more time in tuning and adjusting will only get better!!
I suppose in time I will add the built-in sub in the trunk, but for now this will do