Hi there,
We operate a couple of CJ2 and 2+. We have on some airplanes an Audio Speaker/Headphones and a Headphones only knob. The knob is pretty hard to find: on one of the planes it is located at the end of the EGPWS switches and on another one we have it on top of the GNSs. Go figure out!!!
For the headset: I use a Sennheiser ANR and its working fine. A colleague tried a telex and the first officer was not able to hear or transmit.... i get a continuous tone when we try the oxygen mask mikes. if we have a continuous tone, i usually reset the first officers mike jack and it is working again! (Any logic behind that?)
On the CJ2+, they finally assessed the problem and the audio panel is quite good.
Hope this helps...
LearjetGA