OK, first off, your 6 year old is NOT mature enough to understand the finer details of your marriage, so don't share them with the child. Secondly, NO CHILD deserves to hear anything negative about one of their parents from the other parent, and you should NEVER try to pit your child against your wife in such a manner. Thirdly, don't talk to your 6 year old about your sex life (or lack thereof)--again, this child is not old enough to hear about stuff like that. Fourth, you mention all these crazy remedies you and your wife have tried, except for marriage counseling--have you considered marriage counseling in all this? You guys have 2 children, whom I assume you both love dearly, their parents separating is going to be hell for them both. Do you REALLY want to put them through that? They are going to think you're leaving them as well...you know that, don't you?
I would have a family meeting. You, your wife, and both children. All you really need to say is that "Mommy and I haven't been getting along, and we both feel that things might be better if Daddy lives someplace else for awhile." Reassure the children that you love them both very much (they'll think you don't though), and make yourself available to them as often as you can. Do not tell each child a different story, because the minute they get together, they'll compare notes. So you'll have the 6 year old saying to his/her 4 year old sibling that Daddy moved out because he doesn't like Mommy anymore, and the 4 year old saying that no, Daddy is working someplace else. That's not good for them. Be open and honest with them, but please keep it at their maturity level.
Please, even though you are moving out, please consider marriage counseling. You guys had to deal with an addiction in your marriage, that's rough. Also, your wife has suffered from depression--again very hard on a marriage. You guys need some pretty major help, and it would be best if you receive it from a professional...and not a professional acupuncturist either. I wish you and your family the best of luck, you'll need it in the coming days.