Connect a subwoofer to Comand 2.0

Good day, I have the following problem: I have a Mercedes SL (R230) with Comand 2.0 so with no original Cinch output to realize this I bought a high-low adapter. this hirhttp://www.sound-pressure.de/High-End-UE-Transmitter-High-Low-Adapter An amplifier of the 1200Watt RMS at 2 ohmens is installed. A 12 inch (30cm) subwoofer with 2x 2Ohm which can withstand a power of 1000Watt. And an MDF housing brand own with 30 liters closed. I have the High-Low Adapte r connected to the front system of the SL. Since there are only 2 tweeters on the rear system with me and the bass comes from the doors of the front system. When I take the subwoofer into operation he has a maximum power of about 25%. He runs however not satisfied. If I now from a colleague a cinch cable from his car radio which has an external cinch output for the subwoofer to my amplifier go and take the subwoofer back into operation it runs about 4 times so loud. 1. Either the high-low adapter is defective. 2. The high-low adapter cannot process the signal from the command 2.0 correctly. When searching the forums I found several suggestions for solutions 1. An active high-low adapter e.g. USC from Xetec unfortunately cannot find any more to buy. 2. Soldering the cinch cable direck at the command 2.0.http://www.motor-talk.de/…/Attachment.html?attachmentId=437276 Page 6 Which solution do you find best?