Getting to your ultimate question about the gamut to use for scanning photos.
The short answer is that yes, it can make sense to scan photos with a wider gamut than sRGB. Modern printers can definitely print colors that fall outside of sRGB (in fact, a fair number even exceed the range of AdobeRGB 98).
The only real question then is what colors you have in ...
Color print paper is CMY. We are talking cyan (blue-green), magenta (red-blue) and yellow dye only.
Ink based prints such as ink-jet or dye sublimation use pigments and or dye or both. In these systems as well as lithography fail to produce a "good" black. Thus the prints lack sufficient contrast.
A black hue should form when CMY are superimposed. ...
Anything based on the recording/display of light itself is additive color (RGB) based... e.g. silver halide print paper, film negatives, and film positives (slides), LED monitors.
Anything based on pigments is subtractive color (CMYK) based... e.g. inkjet prints.