I am currently using Vegas Movie Studio 14. I just purchased the upgrade to 15 but have not installed it yet. I am thrilled that I can insert my VST plugins into audio tracks. That has been a real lifesaver! I am experiencing something odd, though. The default "template" has 3 stock plugins - gate, compressor, eq. If I remove them and insert my own plugin all is well, however, if I attempt to insert one more plugin, nothing happens. It just shows me the window with the single VST I have already inserted. I tried inserting many different ones just to see if it was an issue with a particular plugin. Nope. They all exhibit the same behavior.
Is it possible to insert more than one (third party) VST in an audio track?