The Harman Kardon system of the Ascent is built to a price point and is most likely not comparable to the same brand in a luxury car, such as a BMW. I enjoy the sound in my Ascent, but you will typically get a better system in a luxry vehicle.
The X5 ride quality (as a passenger) was no better than the Ascent. I also do not think it’s any quieter, but the Ascent can be loud at higher RPMs, and the engine doesn’t sing as pleasantly as a BMW. The rear-drive biased luxury SUVs also usually are fitted with wider wheels and tires for a nice agressive stance.
All that being said, when it had to replace my 2019 Ascent I shopped around but still came back to a 2023 Ascent. You get a lot for your money, that’s for sure. Subarus are also just a better fit for my style.