I've studied Spanish artillery and am in fact the co-founder of the online group SARA (Spanish Artillery Research Associates which anyone is welcome to join) at:
http://groups.yahoo.com/group/spanishartillery/
but I know very little about Spanish small arms. This piece looks like a very fine, high-grade sporting arm, given the extra embellishments, the once gold-filled touchmarks, etc.
Does anyone know if the maker(s) of this elaborate firearm also made plain muskets for the Spanish Army? Are there any contracts of record between the maker and the Spanish crown?