Customer members plugin/form with Mailchimp optin?

Hi all, thanks for any help in advance.

My client needs an opt in on the registration for for his site. So a checkbox to opt in to his mail chimp newsletter list.

He also needs a custom registration form with extra fields than WordPress offers as standard.

I have found plugins that do these two things separately but not integrated together.

Currently have WP-members set up to handle the registration and members side of things and looked at autochimp for the opt in but can’t put the opt in on the custom reg form.

Any one any ideas?

Many thanks