I have just re-read this thread and appreciate everyone's comments.
My dilemma is a bit different. I own Ivory II ACD and also Garritan CFX. While CFX has been my main piano by a small margin, I am reluctant to install it on my Mac Studio M2 Max due to lagging support. CFX itself is not Apple Silicon native, and I've learned that the correct ARIA Player needs to be chosen carefully. I prefer to avoid installing and maintaining software that may soon become fully unsupported.
This leaves Ivory II ACD. I recall that a version of this has been updated for Apple Silicon; this may be enough for me because I do not need Ivory III ACD improvements. Are there any tricks to running Ivory II ACD on a modern Mac?
Fyi, I hear basically the same things as others here when comparing ACD with Modern D. I slightly prefer ACD for its warmer and arguably less focused sound. In production I've tightened this up with mono-ized bass below about 180 Hz; this helps focus the instrument without casusing significant artifacts.
In any case, comments from Ivory II ACD users who are staying put will be much appreciated.