Memory map:

Something about power supply.

The card in the full version, with LCD display and backlight, may require a maximum of 650 mA of current from the 5V supply.
Therefore, it will optionally have its own stabilizer directly from the 9V supply.
For the OLED display (not need backlight), the total current is between 450-500 mA.
I'm also wondering about the version without the display.
It will save another 50 mA, but will require other software (configuration in the dark ).

The values of current given are the maximum values.
I have to use them to ensure stable operation of the card.
The average current needed to work will be about 30% smaller.

Oh my. I have just checked that the old 64K module consumes almost 500 mA (one of NMOS 4164 may pull at max 48mA of current).
As an option, can be leave an additional power supply.
Yes, step-down DC/DC (LM2675).
By the way, I used it to generate the bias voltage for the LCD contrast (-5V).

If it is don't work then for a last idea I can try disassemble SMD Turbo card... removing ICs, and trying to find types in IC tester.

The encoder can be rotated left and right (unlimited) and pressed.
This is enough to navigate the menu.
Something similar is in this movie.
My idea is a bit different. I want to use a hardware blinking cursor for menu items marking, instead of every time redraw the screen.

Cool
It has only one drawback. When there is no cable, it's easy to get lost

What is the 1 MHz clock signal for ?
Is not it to the sound synthesis system ?
I can output a third channel with a frequency independent of the selected processor clock speed.