The parish registers I have on loan at the moment at the LDS FHC are filmed from c.1794 copies of the originals. I think these are the same films as the ones available for viewing at the Manx Museum.
I may be wrong about this - and hope that someone who uses the MM will correct me if so - but I don't think the original registers were used in the filming, so there is unlikely to be any current access to them for family history.
Sue