Honestly I planned on using both the occult adventures and DSP material for Athas, simply explaining the occult magic is more of the arcane version of psionics. I can see the medium as a shamanistic class, calling on fragments of entities/vestiges of lore and binding them and the occultist as someone who uses items as vessels for their arcane energies. Spiritualist is the vessel for a echo of the past, possibly even a Tribe of One. I can even see the mesmerist being a sorcerers kings best lacky, using their mind probing abilities to really turn the crowds.
Also DSP is producing a supplement that can blend both systems! Theyre so nice :3
Also I think the Akashic Mysteries from DSP are a pretty awesome addition to Athas, I did it with incarnum in 3.5