Have you correctly setup a VST instrument to generate some sound ?
Devices\VST instrumnet menu click a slot and select your VST instrument
Once selected makesure its power button is lit
Back in the track view select the inspector for your MIDI track ( eye looking left )
in the out : channel select you VST instrument
Now when you play any midi recorded on that track you should hear your instrument if not try disabling Direct monitoring under Devices \ Device Setup \ VST audio bay
If you want to hear the instrument in real time when you press keys on your X3 make sure the monitor ( little speaker) icon is lit on the MIDI track
Hope this helps as I'm running
SE3 and the manuals with that are dire too
Rob