Many people are finding that if they assign the MIDI component of their older
sound cards to IRQ 9 that the MIDI no longer works. The same may hold true for
any other component of the sound card.
The APM (Advanced Power Management) and ACPI (Advanced Configuration and Power
Interface) functions of a typical Pentium, Pentium II or Pentium III computer
must use IRQ 9 to work properly. This will conflict with the MPU-401
compatible interface or other components of your ISA sound card.
If you wish to use IRQ 9 for your ISA sound card, it is recommended that you
disable all Power Management functions in the BIOS or CMOS Setup Utility for
Here is what Intel has to say about this:
"IRQ9 is not available to assign to ISA add-in cards because it is dedicated
to the power management function of the PIIX4E controller on the motherboard.
This is true for other motherboards which use the 82371AB PIIX4E component."