I ended up removing the joystick ports from my sound card design, since I would like to have the primary system processor handle joystick input. Running interrupts through the sound card processor to the main processor seemed like unnecessary programming overhead. Given that, I still need a joystick port (or two). For now, I've used one of my generic VIA add-in cards to make a joystick (single) add-in card.
The design is quite simple. I'm using an 8-input AND gate (CD4068BE) on the five joystick signals (up, down, left, right, button) to trigger an interrupt on the VIA. Those same five signals also go to the VIA and are read when the interrupt is raised. Like previous add-in cards, I went with the professional mounting method for the bracket (hot glue gun). đ Also, I didn't have a serial connector that went straight back -- just a PCB mount version. No worries... I ran with it anyways... hence the rise in the cable from the serial connector (in the red heat shrink).
I still have an available VIA port on the card, so I could add a second joystick port. I would just need to creatively mount another CD4068BE in an empty space on the card. At some point, I'll probably design an I/O PCB that includes serial communication (ACIA), a pair of joystick ports, and SPI functionality.