Double monk thin donut is pretty much my combo on every earbud except the cygnus which actually sounds tonally better with monk thin normal foam.I have tried the stock donut foam before but it was quite sometimes ago. So, basing on that memory alone, it fares a bit better than full stock foam. Love the mid bass impact with the untainted treble but it hurts the imaging quite a bit. I will try again later with donut foam. Btw, this is solely basing on my setup. It might work differently to other persons. IMHO
Everything else benefits from donut monks with a second layer on the front but not on the back so it remains a good fit.