We know they can interface with any human cyborg implant, ANY. So that’s a lot of ground covered already. Surgically insert whatever needs to be inserted and the nanites will do the rest.
As for PsiBot upgrades, they’re there to be found. During the height of the war there were hundreds of thousands of PsiBot, now there are a few hundred, if that. All that tech is out there waiting to be recycled, just like every other bit of tech we still have left.