Sorry, my personal bass amp to the audience.
For clarification: bass > new amp with simultaneous speaker & headphone function OR new amp with external headphone amp in-line > done. Sound guy will set-up an array of "ambient" overhead mics which should pick-up every nuance emanating from the pit. No splitter cable required. Word of caution: if your chair squeaks or you fart, the audience will know. Bonus points if the sound tech has assigned delay / reverb.
Riis