The Akai S5000/S6000 series are a bit problematic in terms of stability, they tend to freeze quite oftenly without even giving you the ability to save your program. If you want a computerish unstable sampler with many cool features - get Kontakt, i think it's the best software sampler available today.
However, if you still want to go the hardware route, get yourself an Akai S3200XL (but XL not the regular S3200) or EMU E4K if you'll find one. EMU E6400Ultra is also a good choice, but you can forget about the RFX card because it's way too buggy.
When buying an EMU, pay attention to the data wheel to make sure it doesn't skips data. When buying an Akai, pay attention to the screen backlight to make sure it doesn't fades out. Those are the most common problems with those samplers.
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