Filling gaps between layers of acoustic plasterboard

[pls1]

What is the recommended preparation when applying two layers of Soundshield plasterboard (or equivalent) to a ceiling with Resilient bar in place?
I've screwed up the 1st layer of 15mm to the resilient bar & 2nd layer of 12.5mm is ready to go. I've read that staggering the joints is recommended but should the taper edges be scrimmed & filled first before 2nd layer?
I've got some AC50 to fill the gaps on the non tapered edges but not sure what to do on taper edges to maximise soundproofing.
I tried contacting Knauf as my boards are Soundshield, but still no reply yet!

 

[23vc]

The only thing you're going to be able to use to fill the tapers is plaster, and I really don't think the type of plaster you use is going to make much difference in the grand scheme of things. But there's something called sound coat (british gypsum) which is an acoustic rated plaster. Why tapered boards, assume you couldn't get straight edge? It's a fair question to ask Knauf I guess, but personally I'd just skim the voids with whatever and crack on.