The old Axis X became the current-day Stryker (mostly the same construction, wider underfoot). The old XT more or less evolved into the Recon. The Crossfire evolved out of the old Axis XR, although it shares dimensions, more or less, with the X and XT, but as skis have gotten wider, it is still inteded as K2's all-mountain/frontside ski.
Some comparable skis to the old X would be the modern Legend 8000, maybe a Rossi B78, Nordica Nitrous. Other skis in that performance range would include the Elan Magfire 12, Head iM78, Atomic Nomad Blackeye, fischer watea 78, ect.