I'm looking for some sort of small amp or mixer or other audio equipment that would be able to accept multiple inputs (i.e. my gaming computer, laptop, and my iPhone all at once), combine the signals, and output the signal to my speakers, my headphones, or both. I would also like something that is rather small (no larger than 12"x4") since I plan on attaching it to the underside of my desk to keep it out of the way but easily accessible. I don't really have any experience in audio equipment so could someone kindly point me toward some sort of device that would fulfill these needs? An amp would probably fulfill these requirements but I feel like there must be some equipment that would fit my use case better and be cheaper since I don't need to drive anything with a large impedance .I just need to combine the signals and output them.I'm looking for something that is somewhat premium but doesn't have any features besides those needed for this one use case. Thanks!!!