At first this mission was pretty difficult...now its beyond simple. Even did it on HM with 1 real person rest heroes.
To do HM...we had...
3 monks - 2 heal (standard WoH build) 1 prot (non-bond, used shield of regen)
1 SS w/br
1 SV/MM
1 Defensive Para
1 SF Ele
1 Koss running defensive stances
Pulling is key...making sure to kill the groups quickly enough in the area of the 5 ports...they do respawn..so kill and get the wraiths quick. Since your on NM...you can pull them a ways further then HM...just get a long bow
Its trial and error, first time we did it we died...after that it became so easy. You will laugh
As for shiro...make sure Koss has WB to knock stances off of shiro...with out them, ss/sv combo will just pummle him. Blinding skills for when he goes into impossible odds isnt a bad idea either. Thats when he does the most damage to himself...and to you.
Anyways, hope this helps a little.
-Tiki