NEC: Using Non-Rated (CMX) CAT6 cable inside an attic of a single family home
Type CMX is not "unrated", so that Code section does not apply

Your confusion here stems from a misunderstanding of what the Code means by an "unrated" communications cable.  You seem to be under the impression that it's referring to all communications cables that do not have a special rating (such as plenum or riser), but that's not the case.  Instead, an "unrated" cable has no NRTL listing or associated labeling/markings whatsoever, which means that it is not assigned a type for NEC purposes, and is restricted in its use within structures by the Code section you cited.  These cables are used by telephone utilities for service drops because the utility has its own specifications (Telcordia/Bellcore and so on) for cabling plant and doesn't want to spend the extra time and money making utility cable makers get NRTL listings to prove that the cable has properties the utility is already satisfied about.

Instead, the permitted usage of your type CMX cable is governed by NEC 800.113(L), which permits permits the use of any length of type CMX cable less than &frac14;" in diameter within a one or two-family dwelling.  If your cable is too fat to fall under that rule, you can sleeve it in any Chapter 3 raceway in order to comply with the NEC.  (ENT aka "smurf tube" is the cheapest and easiest choice for this.)