The Mach head units are Pioneer made for Ford, high quality except for the display board. The outputs should be typical for speaker level signals, and not very powerful. Note that the Mach has only high frequencies going to the four door speakers, and only lows to the sub.
The wiring going to the sub/amp is a single harness which plugs into the dash harness, in the right kick panel area. So you can alter the sub ens and not do damage to the main wiring.
There are internal line level signals inside the Mach HU's. I don't know how to identify them, but I have a Mach HU with RCA output pigtails, yet to use though. When I had mine fixed over 10 years ago, the man knew the internals very well, and he located the circuits and installed the RCA outputs for me. I plan to run RCA cables and amps for the speakers.