The PCI-based PC Compatibility Cards support both joystick channels. Many 'enhanced' PC joysticks use both joystick channels to support additional buttons. Since the PC Compatibility Cards have both channels, you can use these joysticks, or with a standard joystick port splitter you can attach two standard PC joysticks.
The DOS Compatibility Cards for the following computers do not support both joystick channels:
Quadra 610 DOS Compatible
Power Macintosh 6100 DOS Compatible
LC 630 DOS Compatible
Performa 640 DOS Compatible