Upgrade max Sampling rate to Match That of Max Of Samplitude Pro X4 and 5 and Sound Forge Pro.
Sound Forge Pro allows up to 768 KHz, are you sure you need to go that high ? 
Remember this is a spectral editor designed for real time editing : each time you double the sample rate, it doubles the computation time.
SL Pro currently support up to 192 Khz (which sounds plenty enough ?).
Previous spectral Layers (5)Could handle Same Sampling rate as Samplitude Prox4 Suite.
And no longer works with Sound Forge Suite.
The max sample rate in SpectraLayers has always been 192 KHz.
I am Using Version 4 Now You Mean 19.2k.Sound Forge pro Windows And Samplitude Pro X4 Suite. Both go above 19.2k.Reaper Max 19.2.Is Cubase limited to 19.2k out ?