Im Daghda in charge of the cauldron of inspiration and Brighid the muse. Anne Ross makes a good case for Maponus (Welsh Mabon ap Modron 'Son of the Mother) being especially concerned with poesy and music, and he is a horned one like Dagda.
I've often wished I could find evidence demonstrating that Maponos was horned. I've never managed, though. In the Mabinogion he (barely!) features as a god of the hunt, but no specific mention is made to horns. I wonder if you could point me to where you found this little gem of information... is it in the work of the author you mention? If so, what are her sources in the myths/in archaeology?