Hey, right now I'm using the stock DT 1990 Foam, but only because they become sibilant with the Dekoni Elite Velours. If you find the stock 770 pads sibilant, I'd recommend trying the DIYAudioHeaven Paper Towel Mod. It's exactly what it sounds like, just cut out a circle of paper towel and stick it between the driver and the stock 770 Foam.

Paper towel is more precise than the foam because it's less drastic of a change, and you can add as much paper towel as you need until you find the sound you're looking for. It doesn't affect anything noticeably except for the peak in my experience.