HiFi Kit Building- have you ever built any hifi gear?

Yes I have. Falcon speakers!

https://www.falconacoustics.co.uk/

I built a three CSS Audio speakers: the Critons and the Torii speakers.  They sound wonderful.

DIY can produce wonderful products that sound every bit as good as brand name if not better.

When you realise the cost of the marketing chain, the layers of each stage adds a markup to cover costs, overhead, marketing, risk, profit, and support services. A component on average gets marked up by 5 to 10 times it's original cost. So a speaker that costs $2000 to manufacture will sell for $10 to $20 thousand.  

DIY eliminates all those fees that don't make the component sound any better. However, there is a great influence by the marketing teams using brand recognition claiming their products are superior.

Speakers, all the time.  For anyone interested in diy I highly recommend a trip to diyaudio.com

My first power amplifier was a Hafler kit that I assembled and put together back in the late 70's.