the EmulatorX uses the cpu and ram/hd. i think the Emulator output is optimized for the 32 hardware asio-channels which are powered by the e-mu DSP but the main peformance depends on the pc CPU/RAM/HD.
it’s hard to compare EmluatorX with Kontakt or Halion coz EmulatorX has better layering/mapping/filter/lfo features in general and simply sounds better than Kontakt or Halion. the developers tryed to adapt everything of their hardware-samplers and improve the emu5 samplesound-format in their new soft-sampler - and your can hear this! i think it’s compareable with Gigastudio … only the EmulatorX userinterface is not the best - it’s not scaleable and the sound-library-handling is a little bit confusing. i hope there will be a big update in the near future.
in general i would say - great sound quality simply needs cpu-performance and if you use the 600mbyte piano in the emulatorX package playing chords and a complex melody line at the same time Emulator needs 10-15%cpu power within Renoise on a P4 2.8ghz