My initial thought would be to make sure the models of the 808 and phaser aren't the stereo version. Running those into the amp makes them mono anyways, so it's a huge waste of DSP.
Edit: Also, can you add models to the lower path (1B, not path 2)? If I want to run two amps in stereo I always utilize both main paths. Amps and cabs take up the most DSP by far. You can then tweak the outputs of each path to mix L and R for true stereo. I'd suggest looking at the templates in the preset browser (I believe it's at the bottom of the setlists) for an idea on what you can do. Spend some time to learn the best-practices of this unit and it really shines.