Whoa. I never knew you could edgegyro -> Dair / Usmash like that.
Only problem is I rarely find myself in a situation where I'm holding a gyro with my opponent offstage, far enough offstage to let me set that up.
It's quite easy to set up actually.
The best way to initiate this is while they are recovering, and they get up from the ledge, you knock them back off by using down b.
That or you can hit them with the gyro toss from your hands or from down by while you're in the neutral to knock them off stage.
You can also do a reverse aerial rush downward gyro toss to make it faster. I plan on making a video soon to elaborate on all of this.
I do this a lot in high level play.
Check this out for a reference:
https://www.youtube.com/watch?v=AS9Hxzt0gjI
Every kill set up in this game was from a gyro setup. And I knew which way he was going each and every time because of the direction ROB was facing when he tossed it.
Hope this helps!