It may be the pitch of his voice coupled with how loudly he's speaking.
Call Amazon and ask how to get help from the Echo team... they are still developing the software etc so may have some good insight.
Try changing the name then Echo and see if she recognises his speech with that waking word.
We have tried all the waking words and still she ignores him so I'll call Amazon and see if they can help in any way. Thanks again Tiddlywinks