Emax

The answer is very simple...

Algoritms. Emu software is meant to work with Emu hardware. Is like when you buy an iPod or any other music device, if you use some other kind of headphones the sound is gonna be way different, usually bad. 

The OS of each Emu sampler is calibrated for its own hardware, if you import an audio file only with the correct sample rate that doesn't mean anything, you are missing the antialiasing filter, that is the one that gives the texture and the quality to the actual sample other than the samplerate. 

EMXP is only downgrading the sample rate but is not resampli with antialiasing/EQ or compression. That is what gives Emu its sound, they really did an amazing job suking the sounds out of the technology back then.