I don't have any advice about the ex-pens, but hopefully someone will. I'm sorry the adjustment isn't going as smoothly as you'd like, but it doesn't sound like it is going bad! Hang in there!
I'd like to throw in my own personal experience. Now, Suki (my cat) isn't another dog, but she did have to put up with Rylie coming home and she's OLD. They started out hating each other (well Suki hating Rylie... Rylie was all tail wags) and that lasted awhile...supervised interaction only.
It is now to the point where they can be left alone with each other without risk of injury to one of them. They still "fight," but I've figured out it is playing. They have the option to leave each other alone, but prefer to wrestle. Then after everything calms down (aka Rylie finally stops trying to lick off Suki's face), they'll lay down next to each other on blankets or with me on the couch. It was all a matter of Rylie not getting so excited when she saw Suki that she wouldn't leave her alone and Suki getting used to Rylie wanting to be in her face.
Sometimes I still worry they aren't getting along well enough for my tastes, but they've struck a balance and everyone seems happy. Trust me, I know it is hard, but things will most likely adjust. They just have to feel each other out.
I have hope they will continue to adjust and get along and time goes on, but I'll be happy with them not killing each other if that's the way it stays lol. I have a feeling when Rylie outgrows her super excitable puppy qualities a little bit, Suki's life will be much easier.
Good luck!