A question for you, what did you use to allow overwriting the sound to the headphones instead of the USB speakers. I too have a pair of USB speakers connected to my 7-port powered hub. I’m going to mount an analog audio jack on the front of the table but I don’t know how to reroute the sound and disable the speakers.
I have my Pi overclocked at 1050mhz, will post my settings later.
I used one of these for the sound – 3.5mm Switched Socket I used a phono extender form the pi and cut the other end off, wired that to this jack, and also my speakers to this jack, so when unplugged it goes to speakers, when headphones plugged, it goes to them..
for the HDMI, I used this Here it allows mounting on the outside of the table and plugging into the Pi, so if my HDMI is plugged in and I turn on Pi, it will goto HDMI, if I unplug, it will goto the two internal screens.