It might not be what you want to hear, but it doesn't sound like he was ready for the responsibility of the 'big boy bed'. If you are using the crib for the new baby, however, you will definitely want to address this issue right away. It might be painful (for you) for a while but if you are consistent the attention-seeking behaviors will become extinct.
If you've determined that his crying is because he wants your attention, not because he has a physiological need that requires immediate addressing....then stop going to him. Let him cry. If you run to him every time he cries, then he learns "crying = visits from mommy and daddy" and the crying becomes more frequent and intense in order to garner your attention.
There is absolutely no need for you or your husband to go get him, engage him in conversation (which only wakes him up and ramps him up even more), and then soothe him to sleep. He will come to rely on you every night in order to get to sleep - now, if your parenting philosophy is okay with that (and I get that some people are fine with that - each family is different and you have to choose what works best in each case) then continue with the chair-sitting in order to make him fall asleep. But since you're asking for advice on how to help this situation, I'm going to assume that you do not want to have to do this every night!
This will likely not be corrected in one evening. It might take a week. He has learned that "crying = mommy/daddy rescuing" so if you do not come, his response will only be heightened - he will cry louder, harder, and for a longer period of time because "the old routine that brought mommy/daddy running" isn't working, so he's gonna kick it up a notch to the next level! Eventually, with consistency on your part, he learns that you are not coming to make him fall asleep thus he learns to do it on his own, and the behavior ceases.