Resident dog not adjusting well to new dog?

We adopted a high-energy schnauzer three days ago and are not sure whether this will work with our resident senior boy that prefers low-energy/ indifferent dogs. We haven’t been able to get them in the same room without them having full on shouting matches. New dog only ever play bows and doesn’t show signs of aggression, but is also not reading cues from old dog. Old dog bares his teeth and growls/barks aggressively (but doesn’t have enough teeth to do any damage and is half new dog’s size). They’ve only ever interacted behind a baby gate, otherwise we’ve kept them separated. The problem is both prefer me and want to be around me while I work or relax around the house, but that won’t work if they can’t be around each other.

I think new dog is not understanding old dog’s cues and is seriously stressing old dog out. I’m worried new dog will always be frustrated being around a dog doesn’t want to play, or that he’ll learn to bark at other dogs to get their attention. Will this get better or is this arrangement already showing red flags?