Can I use the Symphony I/O Chassis just for headphone outputs, without any modules installed? Chris April 22, 2021 01:04 Updated The Symphony I/O Chassis does not function without any modules installed. You must have at least one I/O module. Related articles The Symphony I/O firmware update fails or gets stuck Which I/O Modules may be installed in Slot 2, the upper slot? Ensemble Firewire Impedance Specs Comments 0 comments Article is closed for comments.