I would suggest that the easiest method of doing what you want is with a computer based playback
system. With a computer and an audio interface running a playback
system you could place as many sound sources on
stage as you
mixer or
speaker configuration would allow.
I use both SFX by
Stage Research and
QLab by figure53. Both of these systems would allow you to
play dozens of sound
effect simultaneously and direct them to individual or groups of speakers. I use Sound Forge to edit the effects.
Audio interfaces come in many types of inputs: USB, USD3, firewire, or on board audio cards You would need one that has the number of outputs you would need. Mine has 8 outputs and allows me to use 6 on
stage, one in the booth, and one backstage. I have an Audiofire 8 (no longer made) and a Presonus
unit.
From the interface, you would go either to a
mixer or directly to the amps or speakers.