I always like the fact that the Russians seem to be more keen to try other detection methods on military hardware, such as the SOKS array on subs and the IR sensors on the Sukhoi and MiG fighter aircraft (which are supposed to be very good by all accounts and completely passive too). Can't say I know much about SOKS, other than I believe it's supposed to analyse radioactive traces and other particles in the water to detect the wakes of other subs.
I'm certainly no expert on the matter, but maybe they are a bit like the Germans in WW2 in that respect, more openly accepting to unusual stuff to try and tip the balance in their favour.

Chock