Strange distortion on McIntosh pre-amp's headphones output
I've got a McIntosh C2500 tube pre-amp, paired with a 275 bi-amp (and some Martin Logan electrostats.)
I recently acquired a roomate (lucky roomate, right? :P), and now I'm trying to play games or watch TV at night (the stereo doubles as the sound-system for the television etceteras) with headphones. I shut off the 275, so the speakers are simply unpowered (because the preamp doesn't seem to disable the output to the amp when something is plugged into the ‘headphones’ port on the front, as I'm used to); and then I plug a pair of B&W headphones into the front of the preamp via a 1/4"-to-1/8" adapter.
With the system configured as described … I can hear no voices. I know that sounds absolutely *bizarre*, but … when I play video games, I can hear ambient noise, gunfire, music, all fine; but it's literally as if all voice assets have been removed from the game. (In fact, I contacted the game's support *first*, thinking something was wrong with the game in question. Oops.) When I switch inputs over to my Apple TV and try to watch some television, the sound is super-distorted similarly (although it seems *more* so; I suppose it must be clipping a frequency range that's only applicable to the voices in video games; while the frequency extension in television must be smaller, and it's clipping more of the sound there? I don't know.)
Everything sounds dandy through the speakers. As far as I can tell, this clipping/distortion/oddness only applies to output through the front-panel ‘Phones’ output on the C2500.
What am I doing wrong? D: