I have been curious about these adapters but have not used one. I have a few lenses in each of Kiev-88 screw and Kiev-60/P6 bayonet mounts, and a Kiev-6C body (well, and a Pentacon Six but not fully functional). Arax sells the K88-P6 adapter, and also says that one should install their updated breechlock ring for the Kiev-60 with the adapter - I don't have that which is one reason I haven't tried an adapter yet. Any opinions fromusers of the adapter or the Arax breech ring would be welcome.
You definitely need a rear filter to use the Arsat 30mm fisheye. The filter has a female thread and is recessed so there is not a trivial substitute. I have one filter, and a slightly kooky idea for improvising a replacement: attach a 39-37mm step up ring to the rear of the lens, and a 37mm filter. I think this would work optically (might have to glue the step-up ring on), but I'm not 100% sure it would clear the reflex mirror.