Disklavier

Hello,
I recently bought a Japanese import ('93 HQ300 model, like the U3 
with a disklavier), but I don't have the manual.

The Disklavier playback/record functionality is pretty intuitive 
(mine has Japanese characters instead of English text beside the 
buttons), but I can't quite figure out the headphone jack and midi 
in/out features beneath the keyboard (there's also a switch by the 
midi jacks)...

My piano has the second pedal with the silent feature (push down, 
lock left), but, am I supposed to be able to hear tones from 
headphones connected to the 1/4" headphone jack?

Also, I have a question about the hammer returns.  When a key is 
pressed, the hammer returns to a plastic piece that looks a bit like 
a piston -- it appears the piston retracts, then returns to soften 
the hammer's return.  Well, when the hammer initially hits the 
plastic piston, there's an annoying 'click' sound -- occurs with all 
88 keys... even if the keys are slightly pressed (hammer doesn't 
have to hit the strings).  So I can barely touch each of the keys 
and here a clicking sound without actually playing the 
piano...sounds like a quiet old-style typewriter!  My question:  is 
there a way to replace this style of hammer return with the style 
used on new U1/U3 models today?  I recently visited a Yamaha store 
and found that newer models have replaced the plastic pistons with a 
long piece of felt for the hammers to hit upon return.  Can anyone 
provide me with some help?  This clicking sound is driving me 
nuts....  Thanks.  -kevin