Don't know if anyone who showed interest in this is still here, but I've beaten the entire No Sphere Grid monster arena - Shinryu and Nemesis included. Furthermore, I avoided using aeons unless essential - they were needed for Ironclad, Th'uban, Neslug, Ultima Buster and Nemesis. (Yep, I found ways to beat Vorban, Jumbo Flan and Nega Elemental without them. )

There's a playlist of the battle videos here:
YouTube - Broadcast Yourself.

It includes the entire monster arena, as well as Ultima Weapon and Omega Weapon. I'm working on the Dark Aeons, but so far, only have Ixion and Shiva. (Shiva uses an aeon, Ixion does not)