Ok, I'll try to be as short and to the point as possible and list just the facts. There'* much more to this whole fiasco but I'll leave that for another time.

MB Quart deck
Sony 1600 Watt Amp
12" Fubar in custom sealed box
Hi-Lo line converter switch/ believe it'* tapped in after Monsoon amp
No RCA'* between deck and Amp
Still have Monsoon amp wired in.
Stock speakers.

The low'* sound bad.....the Sub doesn't seem to hit the low lows like I know it'* capable of.

The Audio place said I need an Amp for my highs to be able to use the Sub amp properly and not have it mess up the rest of the sound.
I'm not an audio guy so I didn't fully understand what he was talking about. Can anyone here clarify? Should I have him wire around the Monsoon amp and not use it? I don't want to buy another amp. The system sounds very good other then the low bass doesn't hit very hard.

your treading on tricky waters here with your set up....
the BEST way to deal with this situation would be top run a RCA from the headunit to the sub amp, and not have the stock wiring AT ALL involved with the sub.

You need a signal converter. The RCA and stock wiring are totally different. First of all the power going to the amp needs to be "pre-amp" which means its only pushing out 2-4 watts. I can almost garuntee thats why you wont hit lows good. Because lower frequencys need more excursion which requires more power and youre probably pushing 15-25 watts into a pre-amp input. Thats what probably is making them so distorted.

I have a signal converter....also I would think the signal coming off the deck would be plenty strong....it'* a powerful deck....I think the answer is to tap into it before the Monsoon amp....or run the RCA'* from the deck to the Sony Amp....but I was told it wouldn't sound goos at all....something about the aftermarket amp and sub overpowering the stock amp and speakers...the bass would be too much or something like that...this is soooooo confusing!

thats why they make faders, bass, and treble adjustments in the headunit, and the amp has a GAIN adjustment aswell as a crossover

i still think you should run RCAs from the deck back to the amp... i hate dealing with factory amps and signal converters, its always too much hassle to make it worthwhile

not to mention the reduction in SQ.

i believe that the factory amp will actually reduce the bass at higher volume levels

Yeah, that'* what I've been reading too.....so the general concensus here is to go with running the RCA cables from the HU to the Sony Amp then? I was going to have them try tapping the LOC before the Monsoon amp first to see how that would sound.

yes it will. the mosoon amp will drop bass volume at high volume, and also limit how low frequency will be produced so as not to damage speakers

yes it will sound SOOO much better and actually have the right freq going to that amp instead of messing around with the speaker wires