Thanks to some expertly timed coffee from Ignacio, I have been able to achieve indefnite locks of the DRMI, first on a 1F/3F mix (P:REFL11, S: REFL165, M:AS55), and then purely on 3F (P:REFL33, S:REFL165, S:REFL165). MICH is currently actuated on the ITMs. 

I saved a snapshot of the current settings so I don't lose my settings. I think one thing that prevented earlier recipies from working is that whitening gains may have changed, which we don't typically note down when reporting input matrix settings

My current settings for 3F locking:

REFL33:

+30dB whitening gain, +136 demod phase

PRCL = 9 x I - 200 counts

REFL165:

+24dB whitening gain, +3 demod phase

SRCL = 1 x I, MICH = 5 x Q - 1000counts

MICH: G=-0.03; Acq FM4/5; Trig 2/3/6/9

PRCL: G=-0.003; Acq FM4/5; Trig 1/2/6/9

SRCL: G=0.2; Acq FM4/5; Trig 2/3/6/9

I've injected excitations into the control filter outputs via the LSC-FFC FMS (and notched the frequencies in the control filters themselves), and noted GPS times for offline sensing analysis. (Namely the 10 minutes following 1125398900)

Handing off to pure 3F was a little finicky at first, I needed to use some pretty large offsets in the MICH_B and PRCL_B FMs. (-1000 and -200 counts respectively). Once these offsets were found, the DRMI can acquire on 3F. Alignment is pretty important, too.  Acquiring is much faster when the loop gains are "too high." i.e. I see a fair amount of gain peaking at ~300Hz. Nevertheless, things are stable enough as is that I didn't feel like digging into reducing the gains to quieter values.