Originally Posted by ontopofm
do you installed the line driver near the HU or near the amp in the trunk? I just ordered a line driver bcuz i also some hiss, hope it will reduce the noise
In the E9x with HiFi (OEM amp) you will not have any other option than installing the line driver near the amp in the trunk, just because the wiring and the space to put it is in the trunk.
For example, my old configuration (E46 M3) was:
OEM Nav Tuner -> Matrix line driver -> 3SIXTY.2 Processor -> 6-channel amp
The great thing about the Matrix (if you do not want to create RCA plugs out of your OEM HU speaker outputs then you can use the LC6, it works the same) is that it will give you 6 pairs of high voltage, high S/N ratio (110dB) and gain adjustable outputs out of 4 pair of inputs, so you can individually adjust the front from the rear from the underseat subs OEM HU output gain levels (up to 13V peak) to the aftermarket amps.
You can keep the aftermarket amps and processors gain levels at minimum, thus radically reducing or simply eliminating the "hiss" at the very source.