What do you mean by "the sound quality kinda blows"? Are all the speakers functioning to some degree?
It looks like the 2002 Mach460 uses one RCA to feed the front woofers' amp and the other to feed the rear - the woofers run in mono. There's a couple of ways to hook them up:
- you can just plug it up to the sub-outputs on the headunit but the amps already have crossovers built in set to the correct frequency and slope for the system and you might get phase issues and weird frequency response around the crossover frequency with stacked crossover filters.
- connect them to either the front or back outputs but you lose proper fade control on the woofers
- connect them to one of the front and one of the rear outputs (ie., front-left and rear-right) so you get all the stereo information and still have (mostly) proper fading
- use y-adapters to combine the front and rear left & right signals into one mono signal each to feed the front and rear amps. This is the most correct solution. For best results, you should use true summing cables and not just a simple y-adapter as you could get noise and bad things could potentially happen when one output can drive another but it'd probably be fine.
It may be that you've hooked everything up correctly and it just needs to be EQed - the factory heads have built-in processing to tailor them for the Mach460 system. My Kenwood sounded thin and weak straight out of the box but after a lot of fiddling, sounds great. You will need to play with the EQ for a while to get an aftermarket headunit to as good as the factory head. Boost the lows, cut a little from the mids (4KHz worked good for me) and season to taste on the highs. If it has a parametric EQ, dial in a big, really narrow boost at 60Hz for some kick drum thump. Don't be afraid to play with the EQs and other DSP processing to get it to sound like you want.
