Don't know if it's still the case, but Yamaha used to include that feature on their receiver headphone jacks... Surround sound (DPL) with regular phones... Sounded pretty good (considering)...

I have the Sennheiser DSP PRO Surround decoder for headphones, and when I can't turn up the volume (most of the time with a three year old) It does very well... Haven't heard of anyone doing it in the digital domain, but I also haven't been keeping an eye out...