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 Symphony I/O: Configuring Speaker and Headphone Outputs Can I use Symphony I/O on my iPad or iOS device with Maestro for iOS? Comments 0 comments Article is closed for comments.