I'm not sure about the DC one. Maybe the DC one maps to an even weirder scheme to support analog, like left stick maps to analog pad, and right stick X axis maps to analog L trigger, and right stick Y axis maps to analog R trigger. Weird, but it would work.
Or maybe it isn't analog (never tested one). After all, there is an adapter that allows you to use the Saturn Twinsticks.
And you don't map them. When you set the Saturn VO to twisticks mode, it switches the a control setup that matches the twinsticks' mapping (I don't remember if a similar setup is avaliable in normal modes - I think it is).
The DC version might detect the twinstick's ID and change to a preset control setup.