And I thought 'Cylon Projection' was used only by Angel Six and Angel Baltar. Now it turns out Boomer and everyone can use it too...
Back when Baltar was on the Baseship after New Caprica, it was revealed that all Cylons can 'project'. They can essentially create hyper-realistic daydreams of whatever they so desire. IIRC, the Six that first reveals this trait of Cylon physiology tells him of how, when she's walking through the bland halls of the Baseship, she 'projects' herself into a lush rainforest.
According to the podcast for this ep, RDM thought up the whole idea of projection as a way of allowing for a diverse range of set/locations while Baltar was on the Baseship, while keeping costs low by shooting on location rather than having to expand the Baseship set.
That said, we don't know whether Head Six and Head Baltar are indeed projections. Remember, Baltar's human, so he wouldn't be able to project at all. Not to mention that the internal characters have known things their host couldn't possibly have known, they've been almost prescient in some of the things they've said. Personally, I'm thinking they're plugged into whatever or whomever is pulling
everybody's strings. The one who brought Kara back, the one behind the song, etc.
This season, at least the second half of the season, has to be hands down the best television i've seen years.