+1 to VPElectricity's point (as usual)...
Kioko12, you mention that your next move is to add another sub enclosure. Is that really the best place to invest? Which 1-series stereo/speakers do you have - the sticky PDF calls them Stereo, HiFi, or Top HiFi?
HK Document for 1er Premium Audio
I used to have the Top HiFi in my former '09 135i vert, and the speakers in that system sucked. In a way, if you're starting with the basic Stereo system, that's great, you saved $875.
If you have the basic system, I would guess an amp & speaker upgrade might be next. If you have HiFi or Top HiFi, the amp might suffice for now, and the speakers should be the next upgrade.
BTW, I think the best thing you can do while deciding is listen to as many 1-ers stereos as possible. Go to the dealer and listen to the HiFi/Top HiFi if you don't have it. Ask Safe & Sound if they have done other customer 1-ers, and if you could demo them. And maybe find another stereo shop or two, and demo any cars that they have done. Bring your iPod with your demo songs. Hearing is believing!
(Oh, I just saw your tag line "King Kong in the trunk"... maybe you do need a few more subs...
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