The DB60XG and the MT-32/SC-55 will both receive the same MIDI-data, but as long as you listen to only one of these, you should be OK. I do not expect any conflict or other trouble.

Thanks for reply. I begun to lose hope, that someone will answer 😀.

But I have another question. I read about the MT-32 on this forum and I have found many posts suggesting to use it with those MPU cards. Is it really necessary? Are there games which won't work through a GamePort? Also, are there many games using the MT-32's LCD? I know there was a topic about this, but I cant find it now.

I believe that standard game ports have problems with games that tries to use sysex messages to remap the MT32's sounds. Not sure how many games do that but most Sierra games do and they are also ones that use the LCD too. I'm not sure either if the games will fail if they try to send the sysex messages and can't, or just keep playing with the standard MT32 patches (which may sound wrong). I've got mine hooked to a SCC-1 and can confirm that both devices play at the same time so I have the outputs routed into a a/b selector so I can choose which one I want to hear.

Guess I will have to try if it works. Will there be problems if I connect the Yamaha DB to the Waveblaster header and an MT-32 to the gameport if the game will send sysex commands? Or when I connect the old version of MT-32 to the 'thru' port of a CM-32L unit and run a game, which can't handle the first MT-32, but uses its LCD?

I don't think you should have problems with the waveblaster, my SCC-1 seems to "ignore" the sysex commands for the MT32. As for the 1st gen MT32's, I understand that they can lock up if the sysex commands are sent too fast, but I've never had that happen on mine so I'm guessing mine isn't a 1st gen or it's not that prevalent of a problem.