Word of advice, make sure you SMN has all of the normal summons, not counting Fenrir, to be safe. We went in with a DRG/WAR(me),WAR/NIN,RNG/NIN,SMN/WHM,WHM/BLM, and DRK/THF. As we walked into the battle, we saw the ENM was ice elemental based on Firesday and our SMN....did NOT have Ifrit! If he had Ifrit, we would have one, seeing we got it down to 5% health without using the weakness. Just some advice.
p.s.DRG CAN do this as well as any other DD. I am a Galka and I also did partial tanking, saving the WAR/NIN a few times, so don't overlook them ^^
Spire is found at (K-9). Remember that - it saved us when we had to run for the zone. Before you walk out of the safe-spot near the place you zone in, look closely on your map. Do a <pos> to see where you are and realize the general direction you have to go.