As Trinners said, no transfer is possible to Amex Intl currency cards.
Probably due to the fact that, by all accounts, the application process and financial requirements can be substancially different for these cards vs. the country-specific products (even though they may both be euro denominated). So its likely a new full application would be required.
I also doubt that the UK teams that administer these cards would agree to waive the fee for a new account but I say that knowing nothing about your existing Spainish account or spending. Anything can happen if you are a high enough spender I guess so YMMV (as they say). Phone up, tell them about your spain account and spending and see what they say.