I now have a complete working system with two large scale examples.
which I will post separately. One controls five with_fx wrappers associated with two live loops, with sliding sequences built into the code. Each slide starts from the end point of a previous one.
The second uses four wrappers, but this time they are controlled by aTouchOSC screen.
The two fundamental routines fadeSteps (essentially your fade function) and fadeControl are shown below, in a simple example program.