Excellent detailing work.
I've made pre-amps using 555 timer chips, which are a dime a dozen, to allow to make a pre-amp that I used for matching impedance (Op-amp). This allowed me to use it to give 10 watts per channel for a CD player , 10 watts into 8 ohms, 20 watts into 4 ohms. This seems insignificant, but the same unit allows me too plug in my Bass, or electrified Violin with a 1/4 inch plug, and by flicking the switch, be able to plug this into an ordinary amp, like a Carver cube, which puts out 100's of watts per channel, and with the impedance matching does not blow the amp. It's amazing hearing your bass at the levels of sound that you are playing, being able to play along with songs. There are tons of schematics for that kind of stuff out there. There are sheets that have all the formula's and symbols for what electric components are used, and how they are soldered onto a PCB board you make just by bridging together holes in a universal board.
There are also so many, too many to be listed, schematics for making your own head unit, and just attaching a speaker, either already made, or if you have the carpentry tools, something you make yourself. I design speakers and the tapered 1/4 wave tubes in my home are of my own design. They are holographic in sound, and by tuning the rear wave of the speaker, has a Fs resonance of 26 Hz, all the way up to 18K Hz.
This stuff is easy to do, once you get the basics down. You don't really even need to know how it works, you just need to know what you want, and how to read schematics, and put the stuff together. You can make an amp, using repurposed step up transformers off of EBAY much cheaper than buying one of the same capability.
This is why you are seeing DACS 9Digital to Analog Converters) go for so cheap, as it is so easy to make a unit, it's only a matter of will. If you don't have the money, then you make it yourself.
That is what I have always done with everything, and people who have much more money than me have a lot less as they have to always buy new, and can't fix or make/design a damned thing. The time and effort you put in now is disproportionate to how much more it will be worth in your savings, and ability to scale up because you can fix something that someone else threw out, and costs $6000 to $7000 dollars to buy new. The stack of tube amps I have were all given to me over time, or I found them at transfer stations, realizing what they were and brought them home. My "Harmon Kardon Citation II" amp was sitting on a table, I got it for nothing. It's worth a fortune.
My wife's Marchalll Amps for her Fender Stratocaster (same generation as Jimi Hedrix's guitar) is worth a fortune. I have kept that going for dollars.
If you learn now how to make or repair what you want, you will have it in short order, and for not much money. Selling such units quadrupling your investment leads up to you getting what for now is unobtanium for almost nothing, IMHO.
