1. Should not count the ITMs. On those we can use big resistors / filters to cut out the noise.
2. For the initial LIGO, we used 7 K resistors and the mass was 10 kg. But...the output driver went +/- 150 V.

So we had a max F/m = (20 mA * 0.064 N/A)/(10 kg) = 0.0001. For the 40m, to get the same thing, we would need 40x less current (~0.5 mA). At the moment we have (12 V / 400 Ohm) = 30 mA.

We need to get a spectrum and times series of the required coil current for acquiring and holding the DRMI, and also the single arm. Then we can see where to make noise reductions to allow this drastic force reduction. 

Coil Driver Upgrade wiki here.