I recently invested in excellent Focal headphones with an open-back design. They sound great but are not quite the same as the whole system pushing a wall of sound at you. The fact that you could hear people talking with the headphones on made me think. (This is rare)
What would it sound like with the headphones and the stereo playing simultaneously?
I put on the Focals and adjusted the volume to a nice comfortable level, then slowly turned up the preamp until I could hear the speakers. The headphones are playing through a Pass Labs HPA-1 connected to the tape out on the preamp, so the headphones' volume is not affected by the volume on the preamp.
The sound became really impressive with a light touch on the remote for the preamp and in my optimal lessening position. The bass was filled in nicely; something headphones struggle to do. The high end was as crisp as possible; something headphones do well—best of both worlds kind of thing.
The bottom line is it is a fun little trick and cool with certain music. My wife thinks I am a nut because the whole purpose of the Focals was to lesson without disturbing the house. Of course, the headphones fill the bill when the grand-baby is in the place, but I still rather lesson to the speakers than the headphones. However, this little trick has become a lot of fun.