Perhaps an outboard stereo amp with excellent specs for accuracy and a headphone connection, that doesn't have to be high-powered or have bells-and-whistles, connected to the outputs of the 950 for used recording or a second zone.
I use a Headroom Little headphone amplifier plugged into the 950's tape output. I have two sets of headphones, a pair of Sennheiser HD 600's and a pair of Grado SR 80's. Headroom's web address is: http://headroom.headphone.com/. The current price for the Headroom Little is $259.00. The Headroom Little is a good sounding headphone amp and is very upgradeable.
I've seen stacks of DIY headphone amp plans running around. Several of which have many positive reviews. May want to check into that venue as an alternative.