Yeah, getting that music board to work with Spikeout was one of the hardest things I have had to do. The harness wiring isn't hard but sadly, different manuals show the pinouts differently making it very confusing.
If I recall correctly, Sega Model 2 game Top Skater and Model 3 game Lost World Jurassic Park Special both use DSB2 as well.
What manuals did you get the schematics/pinouts from?
I've got some spare little mixers just in case so hopefully I can get Spikeout sounding great through the speakers on my SR2 cab.