I also have a beautiful 4 year old daughter with DS.
What I personally have to do is slow her down and have her repeat the word and by a matter of deduction I can usually determine her need. She will scream at me if I don't understand so I calmly sit down with her and ask her things that sounds like what she wants. I have had a very high success rate with this. If she can's say it, I will ask questions, have her point if need be, or take me to where she has her request.
She is is in daycare and learns things there that I am not aware of so can be frustrating to disseminate what she wants. I am a single mom and I just start backtracking on things she may have done at daycare or pre-school or at her dads. With patience I have had great success. She is so excited when I understand what she wants. Her verbal skills are vastly improving which helps. I never signed with her either. She just wanted to talk. Course, I am the only one who really understands her.
Follow your son's cues. Try to redirect his attention to a something calming and ask questions or show pictures, even let him point and of course sign language is great too. Just wasn't for us.
Best to you and big hugs to your son. I only have the one child and I have never known a love like this. Totally infatuated and ready to pull my hair out.
But what parent isn't--with any child.
Keep us posted.
Kim (mom to beautiful Dani with DS)