Why do I have an analog output from DCT700?
Yes.
But digital adpaters support analog out only as they only support SD channels.
If you want HD output, you need to get HD STB.
A DCT 700 is an adapter not a STB it only offers RCA and coax connections. If you need anything else you need to get a HD box.
I have FIOS. Doesn't the coax cable deliver a digital signal to the adaptor?