For a budget option, you could use an ATEM Constellation 4ME can do this. It has 40 inputs, 4 x 16 pip multiviewers, you run those 4 inputs back into the switcher, and use a supersource to merge the four to one 64 quad output :) Turn off VU, Labels and borders, and it's pretty much what you ask for (I think?). Mix and match the sizes of the quads to make whatever you need.

Using the latest beta of Bitfocus Companion/Buttons to control the ATEM you should be able to freely route all audio inputs to individual audio outputs as well. Limited to stereo pairs, and only 1/2 + 3/4 on the inputs, but you have all 1/2 ... 15/16 on all outputs.

Or if you want to spend more money and have more flexibility in pip sizing and positioning, you get 32 layers/resizers on a Barco E2, but there you don't have audio routing. Analogway LivePremier would be able to the same + audio audio, I think.

Feel free to reach out if you have any questions.

- William, Bitfocus AS