Shadow King could win this if he were smart. If I were he, I would target Xavier in a sneak attack while the X-Men are asleep and beat him. After defeating Xavier, I would possess him thus adding his psychic powers to my own. Now, even with the combined power of Emma, Jean, Betsy and Rachel, SK would win a psi fight.
Anyway, after adding Xavier's psi to my own, I would go about mentally enslaving the X-Men members who lack the mental defenses to defeat me and then turn them against the very few X-Men whose mental defenses were too strong for me (namely Ororo, Gambit, and Magik). I would, of course, use my psychic powers to augment the power of the X-Men fighting the three X-Men who kept me out of their minds.