Hi, I'm at my wits end with this problem, and I know it's got to be something fairly straightforward. I just upgraded to Platinum recently, and was having no issues. But suddenly I can't get any audio output from soft synths. 
 
I create a fresh new project, I insert a new soft synth (e.g. z3ta+). Select Simple Instrument Track and Enable MIDI Output. Hit "OK". I choose a preset. I go back to the track view and set the Input to my Axiom 49 controller. I bang away at the keyboard a bunch of times.
 
It looks like there's nothing going on at all--no levels showing in the console view.  But then if I got to the Main Screenset, then choose the MIDI tab I can see green level bars when I hit the keys. (This is where the Input is set to Axiom49 and Output is set to z3ta+).
 
Can anyone point me in the right direction--not sure why the MIDI levels are showing up, but the audio output never gets generated.  Somehow I must've changed a configuration value somewhere, but for the life of me I can't track it down.
 
Thanks!
 
--Ian

Is the Input Echo button enabled?
 
http://www.cakewalk.com/Documentation?product=SONAR%20X2&language=3&help=Playback.34.html

enable midi output has nothing to do with it, actually you should leave it off. in your instrument track, make sure your midi input is set to your keyboard, and output is set to your master bus which goes into your sound card's output.

Sorry folks, it turned out to be some kind of OS/audio interface issue. I switched the driver mode from ASIO to WDM, unplugged the interface, rebooted, plugged everything back together and set things to ASIO and all's well with the world.

So, you're not that guy and did not mark SOLVED in the OP?

Funny, I was actually looking for a "Solved" button before and gave up. :)