I examined the violin mode at about 1000.3Hz using a high frequency resolution, and found that it is actually 2 violin modes, both on ETMY, located at 1000.2936Hz and 1000.307Hz.  I have created damping filters for these in ETMY mode 18 and ETMY mode 20, respectively.  ETMY has 4 violin modes within the space of about 0.3Hz, and today I managed to damp all 4 of them simultaneously, as well as several modes at higher frequencies, as shown in the attachment.

The settings that worked today were:

ETMY Mode 11: 180 degrees, gain = 200
ETMY Mode 18: 270 degrees, gain = 30
ETMY Mode 20: 90 degrees, gain = 12
ETMY Mode 12, 300 degrees, gain = 100.

It should be noted that when Mode 18 runs without the others running, it drives all 3 of them up, and when Mode 20 runs without Mode 18, it drives up Mode 18 as well.  So it is best to run all 4 of the damping filters.  

There appears to be a violin mode at 998.82Hz.  I have attempted to damp all 4 test masses at this frequency, at 90 degrees phase, with gain = 25, and have seen no change either positive or negative.  I then repeated this for both ETMY and ITMX length, pitch, and yaw, with gain = 150 and phase = 90 degrees, and again had no change.  I plan to change the phase and try the other two masses, but the possibility exists that this is actually not a violin mode, or doesn't couple well to any of our actuation degrees of freedom.

I have created the following monitor filters:

ITMX Mode 19 at frequency 998.019Hz
ITMY Mode 19 at frequency 997.613Hz
ETMY Mode 18 at frequency 1000.294Hz
ETMY Mode 20 at frequency 1000.307Hz.

I have modified the following monitor filters to make them better match the violin mode locations at higher frequency resolution:

ITMX Mode 13 from 998.09Hz to 998.083Hz
ITMY Mode 16 from 997.78Hz to 997.785Hz 
ETMY Mode 11 from 1000.44Hz to 1000.423Hz
ETMY Mode 12 from 1000.06Hz to 1000.061Hz.

I made the following changes to the damping filter bank to make them better match the violin mode frequencies:
ETMX Mode 13 from 1010.4Hz to 1010.356Hz
ETMX Mode 14 from 1010.59Hz to 1010.581Hz
ETMY Mode 13 from 1009.94 to 1009.932Hz.