See if you can find the port address of your MPU401 device. It should be somewhere in with the settings of the sound driver...in Windoze's Device Manager probably.
My SB Live shows I have an MPU401 (midi) port at address 330 and an Adlib port at address 388.
Then somehow tell your game what that address is for the device.
You may have to resort to adding some lines to your autoexec.bat or config.sys files so the game can find the info it needs about the music port.