What kind of hash rates are you getting on the Dual Miner 2s?   Mine are all 55-57k (sometimes spiking to 60K), for example:
DM 0:                | 55.59K/57.87Kh/s | A:59392 R:  0 HW:19 WU:0.1/m
DM 1:                | 55.59K/57.82Kh/s | A:60928 R:  0 HW:11 WU:0.1/m

Despite using the dualminer cgminer version and giving it the --dualminer-pll 850 options I am apparently unable to get the to run slower or faster, whether I specify 400 or 850, the resulting hashrate is the same.

Running this on Linux.   I wish the same version of cgminer that works on the gridseed would work on the dual miner2 as well...