I run prefilter over the stock intake horn on my 08 M8. Works good, cheap, and drops weight off the hood.
u must have your hood sealed up good or you don't ride in very much powder cuz i tried the exact same thing on my m7 once and as soon as i hit the POW it would bog bad enough it wouldn't move. pulled the prefilter off the air horn and the box was full of ice and water. the small opening in the air horn created enough suction that it pulled the snow right through the prefilter. pissed me off cuz i forgot and left the rest of the intake home so it ruined a beatiful day.