I have a Scion FR-S that comes with (what I feel) is a pretty decent OEM setup. Pioneer HU, 8 speakers, 300 watts, two of them are 6.5 subs with a small dedicated amp. It sounds pretty good for "free" but I added a powered subwoofer to the small trunk just to round out the low-end while saving space. My question is around tuning the sub to match (gain/crossover). I've read lots of threads about it, but am not sure how to apply it to my head unit specifically. The Scion head units not only have a treble/bass +-5, but also an SSP which is essentially an EQ. The three choices are Natural (which I assume is flat), Hear, and Feel. Now I've set both the treble/bass adjustments to flat as well as the SSP to natural, but the sound just seems empty now in many ways. I'm assuming many head units don't come with both options since the threads have just generically said "set your EQ to flat". Before the sub I had it set to Feel and treble/bass both at +4, and volume at 30 (out of 60), and it sounded great with no distortion. Just lacked thump. Which should I leave flat and which should I be tweaking? Add to that the LOC gains and the sub gains, as well as which volume level to shoot for, and there's a lot of variables I'm struggling with.
Info just for kicks:
Head unit model: AXCP-Q14U T10015
Head unit part #: PT546-00140