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.