Question about Audio Upgrade for Mazda 3

I already have a mono block amp and subwoofers from my old vehicle, which i have not installed on my new mazda yet. I don't want to upgrade the head unit because i like the stock look, and i dont want to lose the little display with the temperature/clock/trip computer. What i want to do is upgrade my door speakers and add a 4 channel amp. My question is. With a line out converter, can i hook up two amps? The 4 channel amp for the door speakers and the mono block amp for the subs? Would i have to do anything else as far as wiring or powering the subs? OR can they be bridged together power wise

Yes, a LOC can do what you need. you can split the RCAs with "Y" adpaters or splice the speaker wiring to seperate LOCs. JL audio and audio control make a series of active products that can give you the outputs for all the amps but also have built in equalization...this is a much more expensive path though.

Bridging refers to a meathod of wiring subwoofers to an amp. It has nothing to do with the actual powering of an amplifier. A amp needs signle, power, groud and remoe wiring. The power must come direct from the battery and only be interupted by a fuse at the battery.

The wire size you use depends on the power your amps need. You can start with a larger power wire and slit it into small guage wires once in the car. THis is doen with a distrobution block.

Perhaps I am reading you wrong, but with the level of experience you appear to have, I would highly suggest letting a pro tackle this so that you dont nuke something.

No i was not planning on doing this myself. I was just wondering. In my old car, i had two amps powered by one power cable. They had the power hooked into one of the amps, and then ran another wire from that amp to the second amp. I figured they were sharing the same power. But anyways. Right now i have 500w rms mono block amp, powering two 12 inch eclipse subs. My budget is $700 to upgrade the door speakers and get an amp to power those door speakers and have all of it installed. A friend of mine mentioned cleansweep. But i have not decided which amp and speakers to purchase yet, or how much cleansweep is. Any suggestions?

you can not afford cleansweep on that budget.
If i recall correctly, it is around $300