I think it is always a good idea to hear what he has to say. You don't have to agree with him and you don't have to (and shouldn't) fight with him about it. If he is leaving something out, ask a question that might direct him to what, for example a replacement cost is for something you would generally do, or how much he would have had to borrow to cover a start up cost, etc. Being argumentative is not going to work and it will shut down the discussion and not even provide his view of your situation, which believe me, will be very good to know. Have a dialog. Don't worry initially about an agreement. See if you guys have the same view, the same concerns. There may be lots of things you agree on, and as I said, you may be able to give him things he cares about and him the same with you. Then go back to your lawyer and discuss the areas of agreement, the areas of conflict, what has a work-around, what doesn't, etc. Divorces do not have to be nasty. They really don't. Smart people really can make common sense resolutions without spending hundreds of thousands of dollars.
I remain convinced that if my husband would just sit down and share his concerns with me, and be honest with me, and listen to my concerns, that we could reach an agreement. Too often you have a situation between the parties that is only exacerbated by an issue with the lawyer(s). That is definitely true with my husband's lawyer who very clearly has some serious issues. From the first contact he showed that he was not a neutral focused on a resolution, but rather he over-personalized the case, had no concept of the issues in the case, made allegations that were untrue and for which he had no knowledge, and was not at all interested in hearing how he may have misevaluated the case. An example. He sent my an attorney an email about what he saw as the difference in our incomes and in view of that because my husband had been paying me substantially more, he said that I had been able to pocket huge sums of money and put them in my retirement (never mind that the retirement in question was from a job I left before he moved out and that I had made no additional contributions to that retirement--my subsequent retirement funds were in a separate and clearly labeled account). He then proceeded to say that my husband should only have to pay me the difference in our incomes. Now that makes sense right? That would be a reasonable starting point (still problems, because my income is not predictable and guaranteed, his is, I get paid months after the end of a year, etc.). Except for one thing. He forgot that we have two very expensive children, a minor and one in college, for whom I pay 100% of the expenses. So either his point was that I should have to completely foot the bill for both children, or, more likely, he and my husband forgot we have two children that require support. When that was factored in, guess what, he had been paying the right amount. Did he come back and apologize for the nasty comments about me and his misperception of the case and the facts of the case? Not that I've ever seen. He has taken ridiculous positions like this at every turn and behaved in a completely unprofessional manner from the outset (I have video of his process server breaking into my house while I was out). While not every situation is as bad as this one, I caution you not to start out thinking it has to be ugly and expensive. Because it does not.
