> There is the futzing with the  'scaledVol' value built in to the assorted mix prims & methods, so surely that ought to work?

Yes, but that scaledVol value is already set to change cyclicly (is that 
a word?) in FMSound organ1 in order to modulate the base sine wave and 
give it some timbre. If we attempt to use that same value to control the 
overall loudness, we will lose the timbre. In fact we would need to 
multiply the timbral volume envelope with the loudness one, but this is 
not trivial because the first one uses a loop.


> What would be the 'proper' way to merge multiple sounds with varying volumes? Do you scale all of them? 

Yes, and whether or not their volumes are varying, the sounds must have 
been scaled beforehand to ensure there is enough headroom for their 
superposition. This again is not trivial, because of the way 
interference works: adding two sounds can potentially double the height 
of their amplitude peaks, where they interfere constructively, but can 
also, where they interfere destructively, lead to a lower volume (for an 
extreme example, if you mix a signal with its exact mirror you will get 
a plain silence).

Stef