so the m5 muffler tips angle out differently than the trapezoid tips.
here's my m5 comp package exhaust with standard 550i diffuser
as you can see the inside part of each exhaust opening had to be cut as the m5 exhaust is more inward.
So you do need the m5 diffuser/adapter (as mentioned in the DIY'S) to make the exhaust openings.
I went OEM (got the kit from getbmwparts.com for 230$ (un painted))
once i put the adapter and other pieces in i can swap the actual diffuser part out for any other diffuser made for an m5.
hope this helps.
