Just a quick update, for those who are interested.
My first goal was to see if I could use the existing HU (pioneer AVH-3300BT) to power the front components.. while it does play well at a reasonable volume, it clips pretty badly at moderate volume. I really need to amplify the front stage to get the most out of the speakers (I know, I know..).
At this time, I have one side complete (temporarily mounted the cross-overs in the doors to help with wiring), mounted the 6.5" woofer to the 0.75" HDPE spacers, fabricated a bracket and mounted the tweeter in the stock location (about 35 degrees off-axis in the dash).
Having one side installed, I can already appreciate what the final results will be!
So moving forward, I will continue the write-up covering the progress of the passenger door.
As for an amp, I want to keep the passive crossovers for now and get a 4-channel which I can bridge if necessary.
I was looking at the Alpine MRX-F30, anyone have opinions about class D? I have no experience with type of amp configuration, but I want something linear and efficient.
So it looks like I will be breaking out the oscilloscope again, after all.