My HU has only 1 set of amp out (rear) but i want to add 2 amps: one for the rear speakers, and one for 2 subs. How exactly do the line output converters work? is the Scosche SLC4 good (or any other recommendations)? is that installed inside the dash? and would it be better to put the speaker amp or the sub amp on the HU plugs (and the other one on the output on the converter). and if it matters, the speaker amp would be something with about 50-70W per channel (pioneer t220 maybe) and the sub amp would be a Rockford Fosgate P5002 w/ 250W rms x 2 @ 2 ohms or 500W briged @ 4 ohms