The Custom mode is very messy (virtually useless if you try to control the saturation), while the sRGB and AdobeRGB modes are very good. (The emulation produces better result than many cheaper displays with native sRGB and worse LCD panel.) So, I think it either works with a simple per-channel LUT + a gamut conversion matrix or it uses 3DLUTs. May be it makes sense if every mode (Standard, sRGB and AdobeRGB) uses simple gamma LUTs (one for the Standard [~ gamma 1.74] and one for the other two [~ gamma 2.2]) and the gamut emulation modes uses their own matrices to control the saturation. (-> But this solution is as good as any if done well... You don't really need 3DLUTs if you know the exact TRC and you know it very well if you can calibrate the hardware gamma LUTs...) But it doesn't change the problem that we don't have any software which can control these hardware features.