I run a pretty high end competition level system in My 07. I’m running the factory head unit and pull the RCA signal directly from the head. The signal is extremely clean from 20Hz to 20khz when viewed on an oscilloscope. The Bose amp handles all the crossover points to the various speakers. This is where the bass limiter is active and any other sound manipulation occurs. Replacing the factory head unit isn’t required for better sound if you pull the RCA signal before the amp.
I would recommend looking into CDT Audio for 2 Ohm speaker options. They offer around a dozen 2 Ohm options in various configurations and price points. I run a set of their coaxial speakers in the rear doors for the kids. I have a switch that kills the rears and factory sub for critical listening sessions. The CDT’s do sound louder and clearer than the factory option. Also they’ve never caused issues on the factory Bose amp with the lower impedance.
In our trucks GM offered a more powerful optional Bose “Luxury” amp. These were mainly in the Escalades and Denali’s but we’re available in LTZ’s. This may account for the better sound quality and bass output.
I believe you may have already figured this out. I recall reading about guys swapping their Tahoe Bose amp with the “Luxury” model as an upgrade. I don’t remember the outcome???