I think.well i bought a sony hu. model cdx-gt250mp... have no amps just hooked to four coax speakers. All speakers work fine when on tuner but put a cd in and only front channels work. I have hooked up lots of stereos but not sue if this one needs something turned off and manual doesn't show jack compared to its menu? purchased at brands mart. even returned for an even exchange since i originally bought a gt-230. u guessed it same thing. thanks