Thanks for the responses.
I am aware of Volume Levelling, but perhaps I do not understand its function. I thought Volume Levelling (and the audio analysis it requires) is intended to affect an entire track or album that is non-standard. My problem with dynamic extremes is more subtle than that. My understanding is that if Volume Levelling used an extremely quiet passage as its benchmark, it would bring that passage up to a standard/average level but would dramatically increase higher levels in the track, to the point of clipping. However, if Volume Levelling works on smaller increments of a file (e.g., limited to those that are extremely low level) perhaps it will meet my needs.
I will read the posts you mentioned and also investigate Night Mode. However, if Night Mode has the capability of solving my problem, I wonder why JRiver's representative did not mention it my friend who enquired recently on my behalf. Instead, the representative suggested a third-party plug-in.
With your help, eventually I will get to the bottom of this! Thanks again.