dosatps
I have been living, and have flown, in Spain, have FAA ATP and now JAA and I have found the Spanish system to be against the individual trying to find a job. There is a regulation, of which I have a copy, which states that no person without an EU passport may be the captain of an EC registered aircraft. Never seen or heard of anything like this anywhere else in the world. The way that companies get around it is by appointing you the SIC and having a Spanish "PIC" who may only have a few hundred hours, but since he is Spanish it is within the letter of the law. I do not know what the repercussions will be in the event of an accident or incident.
JAA licence definitely a necessity. If you manage to convince a company to hire you, they can sort out a lot of the paperwork but therein is another problem. In order to get a validation of an FAA licence, you need to do a flight test. In order to do a flight test, a company must let you use one of their aircraft. Catch 22 if you dont already have a company interested in you.
If you are an EU citizen with a JAA licence, should not be a problem. Good luck.