Yeah that "line driver" is made by Phoenix Gold. Its called the PLD1. That stands for Professional Line Driver (1).
What that does: is that it takes the 4.0volt RMS (preout) signal: and it boosts it up to an amp melting 8.0 volts RMS.
8 volts is VERY high for pre-outs, and with that: you're sure to be pushing that amp to its limits. That should quench your need for more bass. I used to use it when I would compete (on a small scale) with SPL competitions, as that maximizes your install power & components.
Brand new (I dont know if PG still makes them) they were around $200-250. I have one that I dont use anymore, for $50 if you want it. I'll show you how to tune it to your system too. 
Its just sitting in my car audio tool chest unused right now.
For the pre-outs: you can use a splitter that will split the singular RCA's into as many as you want.
What I'd do: is use a 3 way splitter (or use a total of 6 single RCA splitters), that way you'll have 2 pairs of RCA's for your full range speakers (1 pair for the front, 1 for the back) and then a 3rd set of RCA's to go to your line driver: then lastly to your amp.
Keep in mind, you'd best carefully tune your system using the gain control on each channel of the amp: since you wont have any other way of controlling the loudness of each and every channel: because everything is run off the same controls (being the single pair of preouts in question)
Make sense? Hopefully you have full crossover controls on all amps you plan on using. That way you can limit the high range frequencies going to your subs (and limit the bass going to the full range speakers) etc.
Without any sort of crossover control, you'll have the exact same signal being amplified to every single speaker.
If this doesn't make sense or whatever, just ask and I'll clarify further.
EDIT: Oh yeah, and another thing is... your sub may or may NOT work with a certain box. Its best to take the performance parameters to a subwoofer box modeling program and see what will work best for the sub in question. Some subs absolutely will not work in a sealed: others will not work in a ported. Its tough to find that out without properly running the subs parameters through that said program. Call it a "dyno run" for your sub if you will. 
But if a sub is put in a box it was not designed to work in: not only will it sound absolutely horrendous, but it may not be operating at its full potential either.
So having a good sub is half the battle: the other half? making sure the box its in is correct for it.
Last edited by Graham_A_M; 11-05-2009 at 09:51 PM.
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