Thank you so much for all of the support and advice.
-ColinsMom: I totally want him to express his feelings and own them. I just didn't want him to hit anymore. We know that his meltdowns are the result of his bound up frustration; they've just been at inopportune times and places, unfortunately. And I could care less what others think when they have been happening, because these strangers don't have a clue from where they stem. Thank you.:)
-gratified3: I just don't want him to get bored; and I want him to know that the opportunity to learn new things is still available for him at home. And he likes doing workbook sheets at times. I have been trying to see where he is mentally (stress-wise) lately as well. I agree with not giving them to him, or trying to get him to focus if he is not in the mood. Thank you.
-masterofnone: I often told DS to tell his teacher if he got hit, etc. and she would take care of it. The 3 of us discussed it; and she said she would; but she didn't to his (nor my DH's and my) satisfaction. We have apologized to him for this; and the fact that his teacher was not telling us everything. We told him that he needed to tell us; but he would just say, "the kids are frustrating me" but not how or why. He did say that they hit; and we had numerous discussions with his teacher. She basically said that she used to use time outs; but now she thought that apologizing was enough. The "fairness factor" came into play, I'm sure. So the teacher was not "handling it properly" - the same as in his last pre-school last year.
-onthegomom and Grinity: I will try the more physical "learning" with him...zoo, botanical gardens, etc. That is great advice; and allows us both to get out of the house. Taking more breaks for snuggles and just concentrating on him and his play interests seems to be helping some. Our reconnecting with eachother and reassuring him that he can trust me seems to help as well. My DH and I aren't at odds with eachother, just at odds in our heads, btw.:) And we don't discuss DS in front of him. Seeking the nurturing social time with age peers is tough. I haven't really been able to find a nice kid with whom he can play. Going to the park with him usually ends with disappointment caused by mean kids; so we rarely go there anymore.
Thank you all again for the hugs and support. All good stuff!!:)

Any suggestions about when to introduce "authority" figures back into his routine (swim lessons, or other type classes? Someone suggested an art class. Thank you in advance!