under the seat stock subwoofer
 

Has anyone upgraded the stock subwoofers?
under the seat.

DIY?

BSW makes some replacements.

I tried removing the grilles in mine by moving the seats in various different ways without success. Maybe it's due to having the multi-contour seats?

I was going to tap into the L+R on each sub and run it back to the trunk for my amp, but after not being able to remove the grilles, I decided to tap the signals at the output of the factory amp instead.

Actually, I take that back. On BSW's site, it doesn't look like they have replacement subs for E70+

I have read elsewhere that the earthquake sxs 8" subs will fit. Seat has to be removed to get the grill off and replace the subwoofer. EQ makes good subs too.

I replaced both of my subs with SWSs. They're made for a direct BMW OEM replacement and come in 2ohm if you're NOT upgrading your amp and a 4ohm if you are. The bass is a little better for my taste. I was looking to get rid of the boominess and was trying for a quicker/tighter bass with better extension control. Boominess is still there but not as bad. It takes a little time for a speaker to break in so it is getting better but I wouldn't expect a drastic change. Replaced all of the other speakers with BSWs as well. It's the cheapest way to go as far as I know without getting into a custom install/upgrade.