Put the device as a midi effect before your Impulse Instrument on a midi track.
The Impulse Instrument has 8 slots controled by 8 notes, from C3 to C4.
Simply choose 1 to 8 (C3 to C4) to define the slot you want to trigger.
Velocity is by-passed and stays identical.
Impulse is great because there are only 8 slots to build minimal sampler with quick access. But 8 isn’t always enough when you need larger collection. Here comes the Drum Rack. The trick is to create many Impulse instruments (ex : one for 1-to-8 kick sounds, another for 1-to-8 snares, etc…) and put them into individual Drum Rack Slots. Placing the device in slots before each Impulse will allow you to quick select between the 8 Impulse sounds without using the boring default midi routing.
For more explanation you can check this tutorial :
Screenshot example :