Trigger samples in live performance

Mainstage has all the software based components you need to play audio samples and receive MIDI signals to trigger them (velocity sensitive, too). Plus you can set up a pad or pads to determine tap tempo. A lot of the e-drum modules have all you need in terms of trigger-to-MIDI conversion (Roland, Alesis, etc). I suggest an audio I/O that had includes MIDI, there are plenty on the market (either USB or Firewire); one box would handle your audio out for the sample playback, and would take of bringing the MIDI into Mainstage.

There are plenty of good drum (and other) samples included with Logic/MainStage; use EXS24 as the sample player. Or, you could use any good drum plug-in such as EZ Drummer or Superior 2 to get even better samples with better velocity layers and more mixing control.

What do you have for an audio I/O now? I find the headphone output jack to be much too noisy for live audio, so you will need some sort of audio I/O. But if you already have one, then you can get by using one of those inexpensive MIDI-to-USB cables you find on eBay or Amazon, which work fine for a drum cable MIDI in. I think I paid $15 or so for mine. In that case, you just plug the MIDI end into your SPD-S, and the USB end into your Mac. Works dandy. I have done this using Toontrack Solo with very good results (using a Roland HS-10 for a pad). If you want higher quality, you might consider an M-Audio MidiSport, but data is data, as long as its the right data.

You could TRY using your headphone out jack, but I find it to be prone to noise when performing under various stage conditions (not its intended use).

If you want to use your Roland pads to trigger samples that are on your Mac, you will need to run MIDI from your Roland to your Mac, which requires a MIDI-to-Firewire, or MIDI-to-USB interface.

Then, you need to get the audio into your mixer/PA, so need an audio interface on the Mac. So, you need a MIDI interface + and audio interface. Some interfaces include both (they are primarily an audio interface that includes MIDI). If you need to go on the cheap, get a low-cost, reliable USB audio interface, and use a MIDI-to-USB cable like I mentioned.

I would figure out what your long-term needs might be (how many audio ins and outs you might need down the road, and how many MIDI ins and outs you might need some day). Then figure out what interface will suit your needs so you don't end up having to trade up if you wind up not having enough ins and outs. For example, if all you are doing is triggering stereo drum samples, you just need 1 MIDI in (from Roland to Mac), and a stereo audio out (for playing the computer-based samples through your PA. So, you could get by with a MIDI-USB cable, and a 2-channel USB audio interface.

Look up audio interfaces on a larger online music retailer like Sweetwater, and read the customer reviews and look at the feature sets to get an idea of what's available. You will also see people commenting on various interfaces on this or the Logic forum.

Yes, this sort of box would handle your MIDI and audio needs. Read as many reviews as you can first, or make sure you have a return period, just to make sure all is good. I have had good luck with Roland equipment, but have not used this specific interface.