Whis is recommended or shall I ask which will give better quality rca outputs for an aftermarket amp/sub setup? Metra wire harness or using a line out converter illustrated on mustangworld.
the Metra wiring harness will not give you RCA outs, its just there to connect power and signals from an aftermarket deck to your existing factory wiring.
If you intend on using your factory Mach deck and want to add subs, you will need the line out convertor like shown on Mustangworld.com.
If you want to change your headunit which is the better choice, get the Metra kit and then use the RCA pre-outs on the new headunit to feed your amps.