Look, you have two options, you go with him direct, knowing that in about 6 months or so he'll stop paying you directly and you'll have no recourse to CSA or you can say "no, you've had your chance to go direct, you didn't want to so now we'll leave this with CSA" - he's only offering anything now because he has realised he might just not be above the law and the might be able to take the money direct. If he still thought there was no chance they could get the money from him, then he wouldn't be making you an offer and shouting now.
He's panicking because even though he's telling you that the CSA won't get a penny from him, he no longer believes that. He thinks this time it might not work and the CSA might be able to take money from him. That's why he's trying to bully you into stopping it - if he really really thought he could continue the way he has been then he would be continue the way he has been, ie. not offering you a penny and treating the whole thing like a joke.
Think about it, it's been years of the CSA chasing him and him doing nothing about it. Now suddenly it's gone legal, I assume he's got legal advice and has been told that he's fighting a losing battle.
He is lying to you, he's trying to bluff you into thinking he's got a strong hand - but by the very fact he is both trying to threaten you and make you offers, suggests he's realised it's unlikely he'll win this one. (OK, he still might, but remember, he doesn't think he will now, that's important.)
If he makes any more threats, call the police.