I don't get it guys. I sold high end car audio equipment for many years and HK isn't all that. It was always a middle of the road, cheap audio equipment. Same company makes JBL and Infinity speakers. Samsung bought Harmon a few years ago.
The speakers in my Signature trim sound pretty good. The most important thing for good sound quality in a car is to reduce the engine and road noises. The SE is pretty quiet so the audio quality is very good. If you get better tires, it will sound even better because of less road noise.
Lastly, you can buy much better speakers than the HK ones and ultimately less money. Bavsound.com has a kit for example.
Crutchfield even sells Infinity and JBL speakers for the F56 which are made by the same company as HK. They sell Match Up too which are higher end and they sell that brand subwoofer for under the front seats.