The drummer for us has a similar setup to what your doing (albeit a little less complicated) and we have managed to get it working for a live performances.
He has a mid range TD8 electronic kit with MIDI I/O out the rear panel of the roland module. We use an EMU 1x1 USB-MIDI converter (£20) into a dell laptop (dual core 1.6Ghz, 2GB RAM, 120GB) and Cubase in this case. Load up a MIDI track and your selected piece of software. At the moment we are using BFD2 (55GB libary) and also Superior 2.0 (the sucessor to EZ Drummer) which are the best sampled drums available.
We then monitor the track so it comes out of the main outs of the soundcard and then into two active DI's (little soundcard has unbalanced outputs), which then converts the two signals into XLR's that are fed into the multicore, which then goes to two channels on the desk. Pan them hard left, hard right and then just feed them through the PA.
To get no feel of latency, we have to use 96Khz sample rate, 128 buffer size
which gives around 3.5ms overall, but obviously uses quite a bit of CPU power. However, as this type of software is all sample based loading, it eats away at your RAM but doesnt drain the CPU of too much power. At the most, the CPU usage was at 65% with the drummer going at it at his best, so basically as long as its a half decent dual core, it'll be fine with a low buffer size. Also, 1GB of RAM is enough for EZ Drummer, but not for superior 2.0 or BFD2. Most occassions we have seen it peak over the 1.5GB size with a moderate size kit, although we do load up most of the kits anyway so that if we wish to change a trigger pad to hit something else, we don't have to wait for it to load up the samples for that kit (ie. Cowbell can be used on one of the toms if you wish)
Others may take a look at this video
http://www.youtube.com/watch?v=0jXntCofC9k
And watch this video about the new Superior 2.0.
http://www.toontrack.com/videos/Namm_2008_S2.0_Demo_640x480.html.
And believe me, these new pieces of software sound amazing. A million times better than those found on the Roland module.
And Neoni is correct about most other professional drummers using triggers. He went to see Genesis a few months ago and they used them then.
