fixed demosong in EnergyXT 3.0

[lucianul]

For those who miss listening the demosong.xt "correctly" in EnergyXT 3.0 , here you have it fixed by me.
In order to work properly, I had to replace the Guitar and Strings synthesizers with one instance of energyXT2 VSTi (2.6).

If I would want two separate energyXT2 VSTi instances for guitar/strings, I would get noise when their sounds overlap.
The fix would be to change the CPU Audio setting from Multicore to Single core.