[TheOtherHobbes]

It was the ancestor in the sense that the DSP features were part of the OS and not a bolted-on add-on with non-standard drivers. And also in the sense that you now had an off-the-shelf machine that could do non-trivial real-time synthesis and processing.

When NeXT was folded back into Apple, the audio classes eventually became (more or less) the AUs in MacOS.

An abstraction layer made it possible to run natively, or on internal DSP, or on external DSP. Aside from Digi, Waves, Universal Audio, TC Electronic, and Focusrite all made external processors that used the AU/VST interface. (UA still do, although recently they - at last - also started offering native versions of some of their plugins.)

[PaulDavisThe1st]

Using AU/VST etc. to run externally was a development that did not happen until later in the 2000s.

Waves in particular, who I worked with in the 2007-2014 era, did not do this until Linux got into shape to allow them to build plugin/DSP servers.