Here is my one-and-a-half cent
The hifi business is similar to the fashion business in many ways. Online Chinese own most of it. Prestige brands make fortunes overseas while their traditional former customers while their days in assisted-living facilities. The once-dominant middle market of department stores and specialty shops is as good as dead. The only segment that's still thriving, besides LVMH, is vintage and resale.
I could see an opportunity for a small business that repairs / refurbs "parts & repair" gear bought for pennies on the dollar, sells it online, and figures out the challenge of packaging and shipping at a reasonable cost. Partnering with a good tech would be the differentiator and value add. Techs are thin on the gound to begin with and more often than not they're incompetent - hence the somewhat abundant supply of gear deemed unfixable.
Run the business from your respective garages. No overhead is key.