My truck is a 21 sierra 3500 hd denali. The bose system sucks. All vocals or really "sound" come from the front dash speakers (2) so the audio sounds so dead! bass is plentiful though. The front door speakers sound like they are inside of a cardboard box, muddy muffled... low-mids. There is no vocals or mid-high's from these speakers. The rear door speakers put out vocals but with fader in the middle they sound like the volume knobs down ~25%. So essentially when in the truck you don't hear them. Long short dealer confirmed its normal, listened to another 21 highcountry, same. BUT my co worker has the bose in his 1/2 ton gasser, I think its a 22 though. the bose sounds good enough all 4 door speakers put out vocals and bass is plenty for me. I wish my truck was like that. I believe the ~20,21's were a one off year. My 08 chev LTZ with bose was not like this at all, was "normal" with door speakers and vocals through them like any other vehicle.
Any ways to the point! I went with crutchfield and they recommended those JL c1-690x,650x speakers and ordered from them, but I also found some JBL series 3 6x9 3 way that the woofer is 2 ohms to try. Last night I popped my drivers door panel off. I compared the JL to the bose, Yep bose is ******, super muffled weird sound where as the JL,JBL sounded clear. But at higher volume levels the JL seemed to clip... odd... I tried the JBL and it sounded better and the cone moved more and was a bit more "clear" but the JL was good too, the JBL took the edge. I was disappointed to find that the system, assuming bose? head unit? has some sort of filter, "all pass filter?". The front drivers door speakers have the mid-highs cut right off. no vocals. BUT yes replacing the speakers will still sound much better.
I never installed them as the metra speaker adaptors have no foam on them so if you install them, they'll rattle in your door so I threw my door panel on for now. tomorrow I'll get foam and at least install my 2 front door speakers. I ordered some JBL 6.5" for the rear speakers too since I was more impressed with the 6x9 than the JL c1's.
I've confirmed-measured that the dash speaker is 4 ohms. the front door speakers are 2 ohms. I'll assume the rear door speakers are 2 but when I get there I will confirm that and update. Crutchfield told me everything was 4 ohms but yeah that's not the case.
I'm not sure what I'll do from here. I wish there was a way to get, or re-introduce the full range signals to the speakers while still using the factory bose amp. Axxess offers their bypass with a dsp to correct it all but thats big $$$$ then again running wiring and power to also install a amplifier and all that fun-not so fun stuff. I figure on the flip side, I'll need to replace the speakers regardless.
That's where I'm at. Will report back with more info as I go.