AMD64 and NPX

[cdsinf]

Hi,

maybe it´s a stupid question, but this is my first time with FreeBSD 6 on AMD64.
Why can´t a make device npx work with my custom kernel? I´ve done it several times when using Intel I386. I´ve noticed it doesn´t exist on GENERIC or NOTES, but I couldn´t find why.
I get 

config: Error: device "npx" is unknown

The only information I could obtain said that my system wouldn´t even boot if device npx wasn´t in my configuration file. And the handbook says it´s mandatory.
Well, it does work, and all seems ok. Is device npx not needed on a kernel built for FreeBSD 6 AMD64?

Thanks,

Estevao