As of the recent era update, the Bard epic, Singing Shortsword should now effect songs in the offhand. It currently does not work as it should. The patch note for this is found here:
http://www.tski.co.jp/baldio/patch/20011008.html
Bards have had their 1h blunt and 1h slash skill caps increased to 250. Their piercing skill cap has been increased to 240. Their Offense skill cap has been raised to 252. Bards are also being moved to the same combat table with all the other melee and hybrid classes (save monks who have separate tables after level 55). Bards Parry skill cap has been raised to 185 as well. Finally, the Singing Shortsword can now be equipped in the off hand and still give full song enhancing benefits.