Reserved - edit

[cidermaid]

Hi Ray, this one had a gloomy and deflated tone to the read as well as the subject.  This might have been your intention, but if so perhaps it was a little overdone...I felt depressed after reading this one!

The muffled room in which we dine   I like this opener, it lays out a clear picture of that type of setting.  For me I almost want to reverse your sentance to read  the room in which we dine is muffled.   (I know this would immediatly would turn your rhymes out the window - just a thought for you to consider - it makes the voice more immediate and less reported)
at tables doomed for eight or nine;    sorry the tables are not doomed...i think you are trying to set an image for the fate of the diners who might sit there, or possibly that this is dining for social interaction - bigger parties and that as a table for two, the emotional overtone is wrong from the outset....but as it is written it is just odd.
the champagne glasses deftly clinked,   As a run on idea from the second proposition of the line above this could work with a change from the to where as the preposition word.
though champagne isn’t what we drink.    But overall this thought then has run on too long and by this line I've lost track of what the opening idea was...more so because of the doomed table confusion.  I think it might be better to put a period in after clinked and make this a flat statement about what is drunk instead.  (repeating champagne referance does not add anything)
The chicken’s textured rubber duck    Sorry this line does not work for me at all.   I am reading the personification of a chicken who has a textured rubber duck!   (Also rubber duck is a huge cleche).   Rubber textured chicken pluck   (I'm thinking that this might add an image of the food being not only phisically tastless but also emotionally not required as well.
and vegetables are overcooked;
rain dribbles down the window-panes;
the walls exhibit aged stains.    The above three lines are all good solid image builders.
The waitress frowns absorbed, remote;   I think you need to address the punctuation for more clarity here.   I think you want The waitress frowns, absorbed, remote.
You shape a sound, you clear your throat   No need to repeat the second you here use and or abandon the syllable count and go for a different effect.  I personally feel that the syllable count is killing the life out of the poem to much and it would benifit from a freer appraoch.
then whisper something indistinct;
our stiltedness makes others wince.
The portraits yawn, the music plinks;
a napkin’s drawn to bloodless lips.
So many seats remain unfilled   If this is missing family members perhaps a further line is needed to inform the reader...as it is we don't know who should be in the seats, or why they are missing.
to celebrate how time is killed.   Killing time is cliche and this variation on this is too close to be new.   (I was thinking that this was a aniversary of some sort, a twist could be added if it is a sad one - a child passing...just my take on the read).

These last six lines have some nice images hidden within them but the punctuation is confused and confusing and the meaning gets lost in this and the off rhymes.  
 

Overall I think this one needs a punctuation overhaul and you need to address a couple of the lines / images to sharpen up your intent to the reader.   But you do have the makings of a nice poem.  As it stands I am reading a failed relationship either due to time or some sadness / event that has robbed them of family / friends.

All the best AJ.