My 98 K1500 sorta has a 6-channel system, in the sense that it drives 2 full range speakers in the front doors (6 3/4” Pioneer 4-Ways) and the 2 full range speakers in the rear pillars (4x6” Pioneer 3-Ways). It also has the two factory tweeters at the top of the switch panels on the doors.
If you think of this as a 6-channel system, it runs everything pretty well. I have a Pioneer 1330NEX unit, which I believe is 50wx4 like the one you want to get. I am also using the GM-D8601 amp for a single 10” SVC sub under the rear driver seat. (Sorry, I dont have exact model numbers at this time. I can get them if needed.)
Now, I have my main speakers running off the headunit with a cutoff of 200Hz on the HPF, while the Sub’s output is 200Hz on the LPF. The result is a very loud, clear sound from all speakers, including the factory tweeters that can be overbearing at times. The sub delivers crisp, clean bass and sounds amazing.
Granted, powering a set of tweeters is much different than powering 4x10” or 5.25” speakers, but perhaps it will work just fine. I have also dabbled in running my full ranges off a 4 channel amp to see if I get better sound, but just haven’t found the need to justify that. Just sharing my success story to add to the thought process.
Edit: Clarified the front door speaker setup.