Before Crunch's post I would have said it was to enhance the rigger/Bassist's performance on stage as part of a mixed rigged/manual performance (as was hinted at in the Rigger chapter.
Now I am pondering the possibility of the Rigger playing remotely jumped-in to said anthro drone.
Along with the Rigger Bassist there will be a physical adept singer, Shaman lead guitar and Hacker (technomancer) keyboardist (playing via AR or VR using the control device matrix action)
Any ideas for price guidelines for such instruments?