exporting 5.1 surround sound

here is my problem…when exporting in 5.1 surround sound…the vocals seem to disappear…all channels are set for 5.1 and i use L/R channel for export as a wave file. I pan the vocals dead center of the surround and guitars left and right rear…drums panned across front left right and center…when i export and play it back in any player that supports 5.1 (vlc foobar etc) thru my sony dh520 …all i get at loud volume is the guitars…can barely hear the vocals at all. have played test files thru vlc foobar thru the sony and all is fine…just the exports of cubase 8.5 thanx