2003 mach deck replacement

From what I understand about the enigma that is the Mach 460 system, trying to marry it to a aftermarket deck via wiring is going to result in speaker ohm issues.

I have a Alpine 9813 with the fully adjustable high/low crossovers and when I first installed it into my 2003 with the mach system I tried several different ways to try to get the best sound. The problem is that the stock tweeters do not have crossovers on them, and they do not run off an amp. I had to install caps (bass blockers) on the speaker outputs on the back of the deck, and then I used the sub preout to get signal to the factory amps for the rest of the speakers. The problem that I had was that there was not enough adjustability on the sub crossover to avoid a large frequency gap between the tweeters and the midrange speakers unless I had the sub crossover tuned off. It was ok, because I could use the sub volume control on the deck to adjust the volume of the 4 midrange speakers independently of the tweeters to try to dial in the sound better. Needless to say I was never very satisfied with the overall performance and ended up scrapping all the mach amps and speakers and installed new gear.