The PrC grants Turn Undead as a psionic SU class ability at manifester level -2, plus any CLE-class levels.
So the PC has
- TU as CLE 3 from his CLE-levels,
- TU as CLE 18 from Ghostbreaker.
- His CHA is 14, so he has 5 attempts/day.
Are the TU-undead attempts separate from each other? Or does he simply have the stronger one?
Since he has a divine feat (divine spellpower), which is powered by divine TU-attempts, he could use the weaker CLE-attempts to power the feat 5/day, and still turn undead 5/day as a Lv. 18 CLE. How would you handle this?
Does this ability stack with a Phylactery of Undead Turning? The CLE-levels stack with the psionic class ability, and the item grants virtual CLE-levels for turning undead. So this PC would be turning as a Lv. 22 CLE.
An orange ioun stone grants +1 CL. Does it grant this to every spellcasting class you have, or only to one class? The item description does not mention a limitation to a single class, but adding +1 CL to two classes of any theurge would be powerful indeed.
The psionics-magic transparency is a common assumption. But in the XPH all ion stones of the
DMG which affect psionics are mentioned individually. The orange ioun stone is not mentioned. Do you think it grants a +1 ML as well? 
The above mentioned PC owns such a stone. Just now I allow it only to add +1 to CLE-casting, but he just keeps on digging me.
