Well, I'm not so sure that the multi mode sounds any different from the dvd mode. In short, the dvd multi mode only works if you have a subwoofer input from the source. I've got a 1212m too, so I just use the dvd mode. I suppose there are a couple ways around this but I haven't tried any of them. All of them bypass the receiver's crossover, which I find to be a great tool, so I don't know if you want to use them.
One is to use the speaker level input on the subwoofer. That would work.
The other is to split a signal from the sound card with a splitter of some type and run that to the sub.
The third, I'm not sure would work at all but seems to be the best option for functionality to me, if it does work, and that's to split the signal at the soundcard and run one set to the regular inputs and the other to a summing adaptor and then plugging that into the subwoofer input. But that may be anathema to some.