After you enter those setting in the dosbox.conf file you then need to manually configure the game to use General MIDI from each game's setup program.
SCUMMVM works completely differently than DOSBox. It replaces the game's engine, while DOSBox gives you a virtual DOS environment to run the original unmodified game.
Base MIDI Settings
mpu401 = uart
mpubase = 330
mpuirq = 9
Samplerate, not needed for your external synth
samplerate = 44100
Tells DOSBox to use Window's built-in MIDI support, and midiconfig is saying to use the device and index 1 which your /lastmidi says your MIO is configured to.
mididevice = win32
midiconfig = 1
In the games you are running in DOSBox you need to select General MIDI, and then choose port 330, and possibly set the IRQ to 9 if it asks you to set one.
You can also use intelligent mode rather than uart for the MPU401 setting, but that's needed for MT32 support, General MIDI devices don't require that.