Well the version of the game I have (Can't remember where I got it as I've had it on diskettes since the 90s when it came out), actually asks me for three different questions regarding sound.
First it asks to play sounds from: and this actually means, play music from... I select the Sound Canvas
Next is that it will ask me to play sound effects from: and I chose Sound Canvas again
Then the 3rd question is to ask me what I wan't to play digital samples from and that only lists sounds cards with DAC ability. But I choose the SB-Pro on that 3rd option.
Now I did get my firmware back yesterday, popped it back into my MT-200 and started up Dune 2. It was better, but it was still dropping tempo when things started to pick up. It first started when the enemy started attacking me with a couple units and I had a harvester dropping off spice. Game play didn't slow down, but the music did. The 2.01 loaded MT-200 also didn't give me any Midi buffer errors like the other one does, but it did have slowdown and just seemed to have trouble keeping up with everything.
To answer your question about the hardware specs...simple. Dosbox .74 with cycles set to 25000.
I was able to prevent the slow down in the music by changing the options so that the MT-200 was only doing music while i choose SB-pro for sound effects and digital sounds. So it would seem it just has trouble handling the music and the odd instant requests for sound effects at the same time. At least in dosbox .74 it does... The specs on the PC I use Dosbox on is an old Sandybridge I5-2500k running at 4ghz. !6GB ram, SB-ZX, Roland UMONE mkII controls the MT-200 and MT-32 connected via Midi Thru (MT-32 was powered off during these play sessions), with a GTX-1070 SC handling GPU stuff. I believe I have Dosbox set to use Overlay for rendering as D3D causes issues with the keyboard not registering multiple keyboard presses at once.
I do have an actual DOS gaming PC but it lives in a closet and hasn't been fired up in about 4 years. Likely needs the CMOS coing cell replaced and the spiders evicted from it. I don't use it because the last time it was on for a really long full day session of gaming, the SB-16 started to cut out after a few hours and stopped playing sound or basically would stop working completely. Reboots didn't solve it, so I suspect the caps on the SB-16 in that machine need to be replaced out.
The LAPC-I inside it likely needs the caps replaced too, but have you seen how many of them there are?! And I don't have a list of all of their values. Still need one for the MT-200 and MT-32 as well but I guess no one has ever though about getting them all together and creating kits to sell.
Midi Modules: MT-32 (OLD), MT-200, MT-300, MT-90S, MT-90U, SD-20