Re: D-Tuna on S1625
Changing pitch on any string results in tension change. So on floating bridge all strings change & you're out of tune. Therefore D tuner is used only on non floating bridges (the bridge sits on guitar body, so it can't drop, when you drop E) and you can only detune notes. On ZR trem, I suppose, you have to use Zero stop to block the bridge.
I have seen only Peavey Wolfgang's with D tuner, and they where all without floating bridge. You saw d tuner on floating bridge? If yes, IMHO it is a really big improvement.