Thank you for that information. I see you are offline at this time and I will be going off for a while as well. If you have any questions on the post below I will be happy to answer you when I return.
The Boxer is doing the right thing and eventually that should subside play. It is possible that the new dog never really learned bite inhibition and your Boxer will teach him that through their play.
What we do with undesired behaviors is turn them around to desired behaviors.
What you can do when you are in the area is teach both of them the cue toy , and when it starts to get rough give that cue. This should tell the dogs to get a toy to play with instead of going on each other.
I would also teach the leave it command so that when the dog does get over anxious then give that command and then the get a toy cue.
Sometimes the spray works , but it has to be reapplied all the time. IN that case you want to get something that you can actually spay it on that will hold the odor. you can get or make a collar cover out of material and spay that. There are also a lot of cloth Christmas decorations that you can get and attach that to the dog's collar as that will also hold the spray. poking a hole in one and sticking some cayenne pepper inside will also act as a deterrent.
I suspect that over time the dog will figure out that play ends when the Boxer yelps which is how they learn among their litter mates.