I know my Silver Monos (90wpc) had the option for cages. It's a KT88 amp, but you can run KT90s in it. The KT90s should be more neutral and have taunter bass than most KT88s which sound thicker or tubbier to me. Think of the KT90 as a "heavy duty" EL34 rather than a Kt88. To each his own.
Aaron
Aaron