I'm having trouble understanding the plugin Mix Modes in the General tab. I see the algorithms in the Wiki, but what do they mean in layman's terms?
They mean: Don't use anything but RC3 for VSTs as RC1 (especially) and RC2 are fucked up. :P Original is using the mixing levels as in MPT 1.16 and is the most useful mixmode for non-MPT modules.
I'm afraid you misunderstood the question (and perhaps others did too).
In the General tab under the Plugin settings, there are Mix Modes for applying wet/dry amounts, such as Wet Subtract, LR Balance, etc.
Just need help understanding how these affect the input.
A mixer is after the input, so the input can't be affected by a mixer-setting.