Thank you both for your replies - I really appreciate the depth of your answer J, and will follow-up on the names link you provide.
To clarify re the 800CE date - I didn't intend to suggest that the direct link is that far back, just that a garbled family story might have connected Ireland and Denmark. 8-)
Yesterday I did a search on "Splan" with the birthplace listed as Denmark. Interestingly, in the light of your posts, the following names appeared: Var Splenden, Splanburg, Splaine, Splawnik, Splind, and Zipliin! It sounds like your suggestions re place names may be right!
Many thanks to you both - I'll post here if I get any more information.