Okay, this is what I came up with.
Contrary to what the JL/SA believes, The X-teams knew they were coming when Meggan detected the surface thoughts of their attackers without intruding in their minds and aleritng the telepaths. What the justice teams happen upon is a very convincing danger room-style simulation with the telepaths on the other side of the mansion creating projecting perfect mental signatures for all the false versions of the X team and Cable, no longer hindered with the techno virus, reinforcing the walls with a telekinetic force field.
The battle between the hard light and robotic xmen and the justice teams goes about as expected while the X teams go down the the heavily shielded lower levels. Just as the justice teams realize they are trapped, the X jets newly installed ati-matter reactors erupt, destroying everything above ground and killing everyone but the Flash, Superman, Shazam, Green Lantern, Martian Manhunter and Power girl. The second Flash stops running from the explosion, Cable ruptures every blood vessel in his body simultaneously. Next, MM is attacked by all of the present X-telepaths, using cerebro super charged by Storm's lightning to amplify their powers a hundred fold. They undo all the work he did suppressing his weakness to fire and convince him his skin is on fire. MM flies off in terror, losing control over his own body.
Before the explosion, Forge, linked with the other telepaths, discovered the knowledge of kryptonite and it's deadly effects on Superman from Batman. Beast reveals that he has been experimenting with a very similar form of radiation for its uses in cancer treatment. Forge and Beast sneak off to an underground lab while Cable fuses every entrance shut and Polaris lines every outer wall with a thin layer of the adamantium the badly injured Wolverine has willingly sacrificed.
With the justice teams' telepaths gone, the Professor and his fellow telepaths pit the remaining powerhouses against each other until Forge and Beast can finish working. Ten minutes later, Forge is teleported to the surface to find that Green Lantern was teamed up on by the other three and killed, but not before badly injuring Power girl. Already protected by a powerful forcefield generator, Forge blasts Superman with a gun that fires the equivalent radiation load of ten pounds of kryptonite with each shot. Superman dies rather quickly, still befuddled by the telepaths. Captain Marvel shakes off the mental control just in time to have his spine severed by two micro-thin flakes of adamantium saved by Polaris.
Rouge is teleported to the surface in time to steal the dying Power Girl's abilities and the rest of her life force, and the Xmen begin preparing to relocate to a new location, since this place is just too well known.