I have spawned this particular named in multiple places. yes this mob spawns in the south tunnel of the aqueduct. from the cenral area , the 2nd static willing sacrifice you come to at location pos 1348 x pos 40 is a ph. the next closest ph is inside the room on the left - the pathing willing sacrifice that can comestimes be right at the door ( nasty surprise for folks when name is pathign around). and pos 1230 x neg 5 is another location. it is a static willing sacrifice facing another static willing sacrifice just south of the 4th 90 degree turn. it is the west facing snake of the pair. I did not get it to spawn at the location posted above ( P 3.7159, -1348.3806, 144.6363, 127, 0, 0, 1, High_Diabolist_Dyengo ), but of course that does not mean it cant.
If you happen to wipe, whatever add-waves you've taken care of won't come back (at least within the 15 minutes we took to re-engage). For example, we killed the 80% and 40% waves, then wiped. When we came back, we only had to deal with the 20% wave.
Dropped the Belt of Forbidden Rites. Doesn't seem to have a big loot table.
HP ~ 7.7 Million Max hit ~ 19,342 Avg hit ~ 7,599 DPS output ~ 10k DPS Nearly 8 minute fight, primarily just dealing with the adds.
Tri-boxed pet-tanked by 100 BST/MAG/CLR w/2x CLR merc and 1x WIZ merc. The 2 adds that he summons are pretty easy, the WIZ merc "tanked" them as they died.