Use the latest installer you have, go to any machine which fits the requirement for the BAS console. Install the BAS console. Install all availible fixes so that the BAS is on the same version number then the other BAS. No Downtime, no serial/srp needed - if you really want only a second managment console.
But BESx is made of more components then just the console and the database: Adding or removing BlackBerry Enterprise Server components - Installation and Configuration Guide - BlackBerry Enterprise Server for IBM Lotus Domino - 5.0.2
(documents ist for BES lotus domino but similar should be existent for BESx)
Maybe read this before installing.