ultimate solution to the hiss issues
I made a long discussion yesterday with my carhifi dealer for possible solutions to hiss problem and further improvement of sound, finally we found replacing the HU is the best choice. He has already installed several Alpine PXE-H650 into system. I have to say I had misconception about that the volume control have to be taken over by the H650 after the sound calibration. It is because the BMW HU has a variable EQ to volume, and the calibration can just act on only one volume stage. I can still adjust the volume of HU but the EQ is no more optimal at any other volume. Even if I add a line driver and DQXS it is the same. The question why I don't replace the HU with alpine CDA-9887 for just 350$ instead spending 800 $ to add line driver + EQ for a moderate sound improvement.
The CDA-9887 has imprint processor fully integrated, has iPod control, USB-Audio, bluetooth telephony, PDC and MF-wheel are all included. Most important is calibration, EQ, XOver all happen at one place, no sonic degrading due to A/D and D/A converting, and no hiss problem any more. With 4x60w of integrated amp I may even just need one 2 channel amp to drive subs. I think I have no reason not to use the CDA-9887. Only one drawback I have to sell both my amps and buy one amp with RCA inputs, because CDA-9887 has only 4V RCA lineouts. Does anyone has a CDA-9887 HU already installed?