I've currently given up getting a DVD9 to boot by itself. Thing is, swapping method works flawlessly.
The DVD9 on its own gives me the 001 (Verbatim DVD-R DL burn@2x). Using the swapping method I have not had a single DRE, freeze, stuttering movies or anything. I find this very strange. How can it be so flawless yet still not boot?
I've played trough the first 15% of story mode, a couple of classic modes completed, some events, wifi play, vs...strange.
Try to burn your iso again and see if you can use +R DL media instead (make sure it doesn't say "made in india"--those suck) and try on a different burner. Also, changing your recording software could really help here, since you seem to have a problem with the media recognition part of the equation, rather than with the readability ("quality") of the burn. Try setting the book type to both, dvd-rom or dvd+r dl. with +r dl media burnt at 2.4x or 4x.
Unless you have a non wiikey chip. Then you may just not be able to get it to work except with exceptionally good burns (hard to get, almost impossible to recomend or predict how to get them) or by tweaking your wii's laser (not a generally recommended solution and one that should only be tried as a last option).