For Kontakt instrument I used two velocity layers and five polyphonic round robin samples per key. By polyphonic round robin I mean, there is separate round robin counter for every key. Key velocity doesn't really matter in instrument's design, but hitting a key really hard make a distinctive initial distortion sound, so I made a separate high velocity layer. The instrument has selectable filters, distortion, LFO and envelope modulators for some creative sound shaping. It requires full version of Kontakt 5.5.1 or newer to work.
Finally, here's a video overview of the Kontakt instrument.