The tips for doing vibrato and dirty ring modulation with the DMM setting are essentially the same as the MOD (Modulated Delay) setting, so check that. There are a couple in reasons you might want to use DMM rather than MOD though.

First, DMM has a slightly different tone because of the bucket brigade emulation. The MOD is a “clean” digital delay whereas the DMM is supposed to sound like an analogue bucket brigade delay which has a bit of signal degradation with each delay. So, final sound is different. Maybe a bit “warmer.” Try it out.

Another reason to set up the DMM mode as a ring modulator is if you want to be able to switch between the MOD delay mode being used as a delay and a ring modulator. This just gives you another way to do ring modulation.