I think that Prof_Pixel is describing the weighting used in a television standard (Rec.709), which I think is only valid for a specific set of phosphors and a certain visual adaptation (ie, to a specified color temperature).

I don't think it's legitimate to use this for densitometry; they're just different things.

The ideal thing is to use a densitometer with a proper visual response. I don't believe it is possible to derive the visual density of an arbitrary material from standard tri-color densities (Status A or Status M).