I need a headphone splitter for my Fiio E10. Do you have any recommendations? will a splitter greatly decrease sound quality?
Check radio shack. I'm not a believer in cables degrading sound however there may be the issue of driving two headphones which I wouldn't think would be much of a problem unless the amp can barely drive them as is. Someone else chip in with any possible degradation.
Otherwise radioshack should have them cheap.
As long as the headphones you are using aren't power hungry it should be fine. The resistance adds up or if they are identical the resistance theoretically doubles putting double the load on the amplifier. If both the headphones are less than 150 ohms you shouldn't have any problems as the Fiio E10 is rated up to 300 ohms.
EDIT: most amps start to distort at higher volumes which is common, so try to keep the headphones as low resistance as possible.