I have been using Vienna Cube with Giga for the past few years. I do not like Giga due to it being unstable. My question is, if I buy GVI or GVI 4, will I be able to use Vienna Cube with it without purchasing anything else?
since the cube is not an instrument but just a bunch of gig samples, you can use it with whatever you like, even kontakt or the linuxsampler. GVI is a VST plugin to your DAW and Giga is a standalone app to run on a (usually) dedicated computer. Giga has been unstable for a lot of reasons mostly because of the way it accesses ram. GVI is a lot more stable in that sense but again its a VST plugin so you generally have to run it as a plugin on the computer you are already sequencing on. Personally I am waiting avec sang et furie for GS4 and I am dreaming about its new 64 bit ram access and hence hopeful stability
Have you turned off File Monitoring in GS3? That's the leading cause of instability. My GS3 setup has been stable as a rock.
And, yes, the Gig files should run on any sampler that supports Gigs. GVI is a great way to go, if you prefer VSTis. You will need to use a host that lets you insert the legato tool for full functionality. You might give Plogue's Bidule a try.
GS4 will also play Cube samples. I haven't heard that the master has shipped to the duplicator yet, so we're at least a few weeks away from arrival...