What you describe requires an FMP developer. The question is whether the current webdesigner is involved.
If you're comfortable with your current webdesigner, is it because they're easy to work with or because you love the end product?
If it's primarily working comfort with the webdesigner, try the FMP developer alone...see how comfortable they are to work with. Friendliness is more common than artistic sensibilities in my experience.
If the webdesigner's end result is what makes you smile, use the FMP developer for the function, then run the appearance aspect past your webdesigner for feedback. Use each one's strengths.
Either way, make sure you get what you set out to get, both form and function.
hope that helps in some way...