There are some threads regarding increasing the ADC sample rate for the Uno. Most of this is achieved via clever pre multiplication alterations to the ADC clock. Has anyone ever just shoved an external ADC chip in front of the Uno?
I’m suggesting something like the Maxim MAX166CCPP. It’s an parallel 8 bit /50kHz bandwidth flash converter. It has a simple connection protocol and there are enough pins on the Uno to interface it. It’s also available in a (proper) DIP package. It’s a little pricey at £10, but might save a lot of programming & debugging effort. The attachment is how it might connect. With some experimentation, you might even be able to eliminate the CS perhaps, which would mean that you can interface with only 9 pins.
Might this have traction?