It might be fun to think outside the box a bit. Given they can found as far afield as North Africa and Iran, who's to say the Undir don't have a form of bagpipes? Granted the Codex version of the Undir bear a clear influence from Southeast Asia it doesn't mean we can't play around with it a bit. My initial idea was this guy's a sailor, been around a bit, so maybe sea chanties? Shaman as I recall (don't have the books in front of me) get perform (sing) as a skill, but I like the idea of having an instrument to accompany my singing. Another idea would be to base the character a bit off the way Will Scarlet was portrayed in the last Robin Hood movie (the one with Russell Crowe). I like the idea of singing bawdy songs at lower-class parties as opposed to upper class ones. They're more fun.
Maybe a fiddle?