Big Dumb 8 String Arpeggios

Playing a two string major 7 arpeggio in four octaves on my 8 string. One of the great things about having all this range is being able to play something expansive and piano-like like this. I think it sounds gorgeous but I'd love to be able to alternate pick it at a higher and more stable speed. It's difficult to mute the lower strings while using an DSX motion because there are more strings to hit with my thumb. The lowest string--mine is tuned to E--also takes more force to stop from resonating. It's generally noisier than a 6 string if not muted, obviously. I've found that I cannot ignore those two lowest strings if I want it to be clean--unlike the lesson with MAB where you conclude that not muting the lower strings on a 6 string isn't necessary--which limits my picking motion a bit.