if you use linux and the alsa sound system, you can not only run multiple sound cards, but you can also break a single sound card down into multiple output streams.
for example most cards made since 2005 are at least six channel cards (three stereo outputs), newer ones are eight channel. with alsa, you can output different audio streams to those channels discretely, or as pairs (stereo). with an alsa add on called JACK, you can also split and combine channels on the fly, simulating expensive audio distribution hardware completely in software.
there is no point and click interface for much of this - and alsa is poorly documented, so you'll need to do some experimenting to get things working the way you want.
edit:
I just read your last message ... you do not need multiple sound cards to have multiple sound effects playing at the same time. any modern sound card will have at least 32 voices, many have 128-512 voices. This is the number of digital audio streams the DSP / DAC can render at once. You just need some sequencing software such as cakewalk, or any number of other packages. most sequencing software will let you assign samples to keys on the pc keyboard (or a midi keyboard), and you can set options like repeat, delay, infinite loop, etc.