for me personally, i would simply use this type of machine to trigger sounds from other modules/vst hosts via midi
a 450mhz g3 or g4 can easily do midi + audio recording.. keep VST cpu hungry devices out of the picture
OR
use it as a vst host for 1-2 specific vst's triggered via midi from another pc.
thats the best use.. that will provide solid reliable performance.
for example i have alpha juno synths and imlacking the actual pg300 programmer unit for it
but theres an app called alpha juno control for X that lets u adjust the sound of this synth..
it also accepts midi in, so i can record midi automaton data TO the alpha juno control to do sweeps
and do sound design by adjusting the parameters of this app which then relays the midi data to my synth
great stuff;)
u can use vst's on a g3 too if u create your sounds and then freeze the tracks or export the sounds..
its all how u do it.. if you are intelligent u can find a way to make anything work
using this g3 with external hardware synths via midi is the best way to use it..
and thats what the production world was doing still in 1999 the emu romplers were everywhere..
like the emu proteus 2000 modules... midi in.. audio out.. play notes.. record.. adjust midi parameters
this is the best way to produce with a g3... using external gear via midi and its what the powermac g3 does best!
even at 350mhz this is more than enough for this..
g3 + audio i/o + midi i/o + hardware + midi cables = realtime music production without VST
i dont really understand the original posters goal to not use a midi interface with this mac..
my whole interest in mac's is mostly to do with their compantibility with cheap affordable midi interfaces from the past
(that stll work amazingly despite their age!)
dont try to use vst with these g3's unless its as a standalone vst host for 1 vst piping its audio to another pc/mac
unless its a basic drum sampler such a battery or lm4 or very weak cpu requirement vst
thats my suggestion