Here is a quick rundown of how to incorporate digital sounds into your acoustic drum setup.
The easiest, and perhaps the most visually obvious, blending of acoustic and electronics is the use of sample pads and percussion pads. These pads are mini kits on their own and easily lend themselves to any hybrid drum kit setup. A sample pad such as the SPD-SX has hundreds of sounds already built in, but it also allows you to sample (record), import, and trigger any sound. A percussion pad typically allows you to trigger the internal sounds within the instrument.
The second method for triggering sounds is the use of additional drum pads around your acoustic kit. These could be in the form of rubber pads, mesh pads, or bar pads in conjunction with your sound source.
The third and stealthier method of triggering sounds is the use of drum triggers. Like their pad counterparts, these triggers also need a sound source. The obvious difference with drum triggers is that the sound is mixed with that of the acoustic drum.