The morals of FAI theory don't mesh well at all with the morals of transhumanism.

It's not clear to me that a "transhuman" AI would have the same properties as a "synthetic" AI. I'm assuming that a transhuman AI would be based on scanning in a human brain and then running a simulation of the brain while a synthetic AI would be more declaratively algorithmic. In that scenario, proving a self-modification would be an improvement for a transhuman AI would be much more difficult so I would treat it differently. Because of that, I'd expect a transhuman AI to be orders of magnitude slower to adapt and thus less dangerous than a synthetic AI. For that reason, I think it is reasonable to treat the two classes differently.