How do the last two channels differ from the rest?

[jwt27]

I noticed some presets in the existing drivers have a bit that prevents them from being loaded in the last two channels. That would imply that these are missing some features that the other channels do have. What is the difference exactly?

[freq-mod]

Perhaps it's related to the rhythm mode somehow?

[jwt27]

I think I may have an explanation. Since you can't trigger the key-on bits at exactly the same time, it's practically impossible to get both op pairs to be in phase. If the second op pair is modulated by the first, then notes allocated in these last channels will sound very different from the rest.