Thanks for your “advice” and your generosity on my behalf

. While I’d happily give say a £50 charity donation out of any financial gain, I’m not going to be sitting down with a calculator and working it out and then handing over any excess. Of which there might actually be none given spend trajectory…
I didn’t buy the system “just to sell it on”; I can use
eBay for that. I bought it out of curiosity, to fettle (or get fettled by people who know what they’re doing), to share something “different” (apparently not), and then to sell on.
Finally, as Nick @Nopiano says, this would not constitute commercial gain. It would be personal gain. You might have a problem with gain of any sort but my hifi fund has benefited over the years from this, to the point where I now have a system I wouldn’t have been able to afford without sensible experimentation. I’ve probably heard more kit in my own home than many, and it’s been fabulously rewarding in aural terms - it’s been financially rewarding too but modestly so and as nice side effect.
Glad to have provided a case study anyway!