Pre-out voltage and gains on amplifier

Firstly I do think I understand how pre-out voltages and the gain knob are used...



Please no comments on choice of equipment either. I had my Eonon head unit hooked up to an active sub and it worked fine, but swapping to a different active sub (which I was expecting to be much louder) was much more quiet even at maximum gain. The seller told me this was most likely my pre-out voltages were too low for the input sensitivity of the amp in the active sub, so the gain knob isn't allowing to set the proper gain level.



So I'm planning on doing a full install with an electronic crossover, which doesn't have a gain knob but does have a fixed voltage output higher than the Eonon, I tried test installing this to boost the voltages to the sub amp and yes it did then work as desired.



So my question is, is the line driver/crossover merely masking another issue, and will I have problems with clipping, or is this the proper way to fix this problem? I've heard many people saying they're a waste of time and make things worse but it fixes the issue I have!



Also where is the usual place to fit line drivers, I was planning under the boot floor but I've read they should be fitted next to the head unit which would mess my plans up!!



Thanks