The first hack everyone does to the Spy Trakr is to install a headphone jack. I jumped on the band wagon. My biggest issue was the mic-speaker feedback when I had the Spy Trakr next to the remote; LOUD!
So I opted for headphone jack AND a volume knob.
I carved out a slot in the right grip with a soldering iron (it is a sin, I know) for the jack (ebay 5-pin) and a small wheel potentiometer (Radio Shack 271-001). This 5-pin jacks automatically switch from speaker to headphone when you plug it in.
This is a crude wiring diagram. It is sad how long it took me to figure it out.
This is a shot of the holes and where the stuff fits in the remote.
The components assembled and awaiting final gluing.
The final installed setup.
The speaker shuts off when the headphones are installed.
Speaker: the wheel controls the speaker from NORMAL to mute. Not a lot of fine control.
Headphones: the wheel controls the headphones from REALLY LOUD to NORMAL.
Overall, I am happy with the results.