The doors are what's hooked to the ANC (if you have it) and can become an issue with aftermarket replacements.
The dash speakers are in parallel with the front doors but don't seem to affect the ANC so swapping them is straight forward.
I'm not sure how the HDs are set up but if you have the base 6-speaker audio look under your driver's seat. If there's a box there (looks like it might be a small amplifier) then you have ANC (that's the ANC unit, not an amp). If there's no box then you don't have ANC and the world is your oyster to drop in aftermarket speakers all around (with adapters) and keep on truckin'.
The base audio speakers are powered from the head unit so there's no external amp.
For just speaker replacement here are a couple of threads off the top of my head:
I literally spent over an hour trying to find this answer, so please don't come at me for not searching! I have BASE stereo (6 speakers) and want to do a simple speaker swap. The other threads out there got SOOO much input that finding this answer has become about impossible, too many people...
5thgenrams.com
All you need do put your base 6 speaker system on steroids is 4 Pioneer TS-G690 for front and rear doors and 2 pairs of Metra 71-050 speaker adapters and you are set !!!!! Don’t worry about changing the dash speakers out as I’ve already tried that with the Infinity and FaitalPro dash speakers...
5thgenrams.com