That's because Flexi and every other piece of specialist sign making software is a pi$$poor copy of Corel... as you've just discovered with CorelTrace the features and tools in Corel are the real deal... they're good, they actually work.
Back in the day specialist sign software was still DoS based when Corel had already made the jump to Windows O/S. We had Corel V3 and the only specialist sign software around at the time was Signlab... and that was Green Screen DoS technology. If you look at the time line Corel got their first so everyone else took their "inspiration" from what they were doing.
As far as your setup goes I'd dump a couple of hundred bucks on a secondhand Dell with XP preloaded.... stuff flexi on it and hook this machine onto your cutter. Design all your files in Corel; you can set the page size to the size of your vinyl cutter then simply export colour seps in AI format to your cutting computer. Use flexisign to haul in the AI files and then simply use flexi to run the plotter. This is what we were forced to do back with Signlab and it's what we've done ever since.
I agree with Wayne that using flexi is a much more easy solution.. you could print from corel but it's easier to use flexi as a bridge seeing as you've already got it. We use signwizard which is 95% cack... the ONLY good thing is the plotter manager function which used to be sold as a standalone called PlotWizard.