but my GX61 can't control its playback and recording, does anything I still have to setup by my own?

Have you went throw setup procedure? I mean installed "DAW Integration", enabled MIDI inputs and put Nektar plug-in into Sonar Control Surfaces?
 
I do not have the device and they do not provide downloads for unregistered users. So I can not really check. My point was simple: if it works for X2 it should work for Platinum.

parco
but my GX61 can't control its playback and recording, does anything I still have to setup by my own?

 
As azslow3 said, you need to register the keyboard on the Nektar website.
 
Once you log in, there will be a 'my downloads' section at the top of the website.
 
Then you select the OS & it will show you all of downloads for the controller you've registered that lists all the DAW's it supports.
 
My LX49+ works very well in SonarPlat although there seems to be a minor issue with the integration, unless its PEBKAC at my end.
 
Using the 'Inst' button on the keyboard to open a soft synths' window will open it, but it seems to be the synth that's highlighted in the synth rack, not necessarily the one on the currently selected track.
 
I was only playing around with both when it did this so will need to do some more testing to see if it's user error on my part, or a bug.

MoodyB
Using the 'Inst' button on the keyboard to open a soft synths' window will open it, but it seems to be the synth that's highlighted in the synth rack, not necessarily the one on the currently selected track.

Sonar does not expose the way to find the Synth associated with selected track to Control Surfaces. I have found a "workaround" using one bug... But I guess Nektar was not looking for "handy Sonar bugs" when they was writing the plug-in

 
I finally got around to dragging my still in the box LX88+ out from under the couch where Santa left it.
 
I'm not much of a pianist but, up until last spring, have always kept my childhood 60's era console upright to noodle on every once in a while.  So I'm only used to real wood pianos.  This latest keyboard is to replace the piano and acquire a comprehensive midi controller.
 
I realize that the LX88+ does not intend to emulate a real piano keyboard, but I find it quite a bit different from what I'm used to.  I find it very difficult to control the volume of my notes.  On a real piano I have no problems, but suddenly some notes are hardly heard and other too loud.  I've played a bit with the velocity curves and have also noticed that response varies between software pianos (DSF Vol.1 Yamaha Grand for DimPro doesn't sound anything like a Grand to me, and is kind of dead, but I haven't explored the different flavours yet).  The included TruePianos is quite a bit better.
 
Has anyone else experienced this lack of control when going from a real piano to a synthetic semi-weighted keyboard ?  Is it something one gets used to quickly ?
 

I can't speak to the differences between a real piano and the LX. I have noticed a great variation between soft synths and velocity action - not only on each key but the balance across the keyboard. So far, I have found the Air MiniGrand and Velvet88 to have the best balance, with some slight gain tweaking, for my playing style. BTW, I've always had synth keys or semi-weighted keyboards here so YMMV.

Most MIDI keyboards do not attempt to imitate real piano. Some have Hammer mechanic which is such imitation, but normally "lightweight". May be the only exception is Kawai VPC, but the price is the weight (30kg vs 10-12ks for most other MIDI boards with hammers).