Force a download WITHOUT readfile??

Is it possible to force a download with using readfile?

I'm currently using header("Location: abc.com"); for redirecting of
all my files to a high-speed file server elsewhere on the internet but
I couldn't get it to force a download.

I can get it to work properly when I use readfile, but that means the
file travels from the high-speed server through my server and to the
user downloading it whereas using the header("Location:"); allows the
file to download from the high-speed server directly to the user.

Pretty much all the comments I've seen state that if I want to force a
download, I have to use readfile.

Is that true?

--Matt