I wonder, why don't you need to pay for FMOD in free version of Unity?? Oh.. sorry, my bad, this things are incompareable... In gamestudio you need to pay even to get proper sounds (is extra version free? I don't think so.)
If you want unity features - use it. You can't just randomly compare things - especially when jcl wants to make 'any' money with gamestudio - but that's something economical.