if m42 is naught but a blob in the 10" then there is something seriously wrong with the scope. as mike said the collimation is probably way out... and i mean wayout. i can have the collimation out on my 8" dob and still get great views of m42. you need to re check it or have it checked if you are having problems.
but the c8 sounds like a great scope
wish i had one! i'd swap my 8" dob for a c8 at the drop of a hat...