I'm thinking maybe I got a bad masterlink.. I'd check yours to see if the clip fits into the grooves on the pin.
I just took off my Regina O-ring and kept the masterlink, luckily. It worked fine, I just used the rubber rings, clip and new side plate from the new DID masterlink on the old main part. If there your masterlink doesn't work either, a Regina o-ring masterlink will work fine.
As to the chain press tool, it wasn't matter of the pins not coming through far enough. A chain press tool wouldn't have made any difference. It's the grooves on the pins being too small for the clip, any clip. Whether it's on the chain or apart in my hand, the clip won't fit into the grooves.