It wasn't his job to speak to them even if he could and as far as meeting them he would have been there when they were interviewed watching the proceedings and liaising with his officers. Clearly the McCanns were not aware of him or what he was such was their state of mind.
If Amaral had personally observed them then IMO he would have explained how he did that. But not a word. He certainly did his best in his book to disguise the fact that he'd never met them, also during TV interviews etc when he didn't give a straight answer when asked. Why the reluctance to reveal that info to the public if he had no problem with it?.
Common sense alone dictates that actually meeting and speaking to potential suspects face to face would be advantageous to a policeman trained to observe - rather than relying on the words and opinions of others.
Why he would want to deprive himself of the opportunity to make his own professional assessment of the McCanns - I have no idea.
AIMHO