It turns the pre-outs off as well, so you'll need to use the pre-outs for a headphone amp too. If you're already using them for speakers, you can use Y-cables, but you'll need something else that will detect the headphones in the wallplate or whatever that you use and turn off the other stuff. I would recommend doing so via an amp with 12v trigger rather than by muting the signal to the input of the amp, but that would more or less work too. You either need an integrated system or you need a wallplate that exposes the same sort of switch inside the headphone jack like receivers have inside. You can use that to control a relay (preferably buffered with a transistor - I do not like driving relays directly from 12v triggers) which could control the amp for the main speakers.
"Vintage" is good for wine, not for A/V equipment.