I doubt that at the variety of transceivers, sound cards and the software use, and propagation effects, that a measure of IMD from a digitized signal from a PC sound card is of much use for an IMD report.
Has anyone compare your digitized receive spectrum to that from a Spectrum Analyzer? I no longer have access to one since I retired but it would be nice to see the results be published here.
I judge the signal quality by the signal bandwidth (width), and number of IMD products (spurs).
We might consider something like this:
A. Typical 70 hz width and no observable spurs you are a XX9
B. 1 set of spurs XX8,
C. 2 Sets of spurs XX5.
D. If you really wipe out the band you are XX1
73 de KC2QFR Fred