Note that LED digits are LED matrices too. MIDI Box SID uses a real 8x8 LED matrix.
If you want to combine a switch matrix and an LED matrix in one project, it will be easier to use “sm example1”. The superfast version may use tricks in the way it handles DOUT that would make it hard to do two different things with DOUT.
mmm you man using the same hc595 for switch and led?
I was thinking of using the same shift register string but different pins for switches and LEDs. Now that you mention it, the “selector” output pins might be sharable between switches and LEDs. So you might be able to do 64 switches and 64 LEDS with 16 output pins and 8 input pins.