Originally Posted by WBS
The balrogs were former Maia were they not?

I find all sources support this undisputed.
Radhruin never claimed they were not: he was clarifying that the maiar-who-became-balrogs used to be maiar-who-were-spirits-of-fire. Of interest, perhaps, is the fact that, although serving Manwe and living in the gardens of Irmo, Gandalf (as Olorin) was himself a maia-spirit of this ilk: perhaps Gandalf had many personal reasons to be both glad of the 'loan' of Narya and, at the same time, extremely wary of coveting the One.

HoG