So many questions. I have a 2020 with the premium sound system, so it already has functioning rear speakers and subwoofer. Honestly, the sound quality is pretty good overall, especially after putting some damping material on some of the panels.
I have no idea whether these Hansshow offerings would be helpful to me or not, especially given the price. Having access to a single 31-band EQ for the system would be nice, although it would be even nicer to have access to a per-channel parametric EQ that included active crossover adjustments. For example having LPF and HPF on each channel with up to a 48dB/octave Butterworth filter on it, and some true parametric adjustment between those bands.
My biggest issue with the stock system is that it really seems to lack headroom. It doesn’t really start getting loud until the volume control is almost all the way up, and at that point it seems to start audibly compressing dynamics, as though the amplifiers are running out of steam.
No idea whether the Hansshow offering is any better or not. Of course they will say it is, but it would be nice to know why and how.
This isn't the product for you. To get the top 5-10% out of your current system, you'll likely get this kit or go see a professional: