rocker41,
Sorry for the late reply (hey, I've been making music in the precious little spare time I have had!)...
It sounds like if you want to install X1 (having misplaced the discs), you will need to download the FULL X1 installer from your account at Cakewalk.
As Jonesey said, you will NOT be able to install the 8.5 version then upgrade it to X1, but you WILL be able to get to the last build version of 8 (8.5.3) using that method.
But - even though I still have it on my system - I rarely use 8.5.3 these days... I am too enamored of the functionality, gui and everything else that is X1 to leave that environment unless I have to (such as older projects created with 8.5 that don't import well into X1 for various reasons).
(And a shout-out to the man from Bristol who has saved my (DAW) life more times than I can count... Thanks, Jonesey!)
Joel