It sounds decent. I am coming from a ported 10" setup (200w) in one of my e30's and a sealed 12" setup (900w) in another so you have to take that into consideration. I also have it paired with the factory DSP/headunit so I don't have all the adjustability I would like either.

But that said, it is decently punchy and can keep up with the mids/highs of the factory setup. Low end is a little lacking, but anywhere north of ~60hz it's pretty solid. For the amount of space it takes up, it is a great option for sure. I am glad my truck came with it, though it was tuned so badly at first, I didn't even know it was there. If you are interested in how I re-installed it check out my thread... I redesigned the factory CD changer/BT/etc brackets to hold the BSW amp so it looks like a factory piece.

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2005 X5 4.4i Build 04/05 Maintenance/Build Log
Nav, Pano, Sport (Purchased 06/14 w/ 109,000 miles) (Sold 8/15 w/121,000 miles)

2006 X5 4.8is Build 11/05 Maintenance/Build Log
Nav, DSP, Pano, Running Boards, OEM Tow Hitch, Cold Weather Pckg (Purchased 08/15 w/ 90,500 miles)

2010 X5 35d Build 02/10
Nav, HiFi, 6 DVD, Sports Pckg, Cold Weather Pckg, HUD, CAS, Running Boards, Leather Dash, PDC, Pano (Purchased 03/17 w/ 136,120 miles)