The marketing of stereo equipment is as funny as the marketing of tennis rackets.
When I was a kid, I upgraded the 6x9 rear speakers of my parent's car with speakers called MindBlowers. I think I bought them at Bradlee's which was sort of a Kmart type chain in New England for about $40. They had 30 watt amps attached and were extremely loud/obnoxious which was the whole idea. They were made by a company called Tenna, which was an OEM and aftermarket audio equipment manufacturer out of Cleveland. I think their components were actually made in the USA; imagine that. They went out of business in the mid 1980's. Later, as an adult, I worked in the OEM audio system industry for a number of years.
The typical OEM car system is quite good now compared to what it was in the 1970's/1980's and before. Most don't require upgrades unless you really want to get nuts with subwoofers, etc. Not really worth it IMHO but to each his own.