I have final results to report after further analysis.
My findings indicate that Beethoven's 9th Symphony ripped by dbpoweramp is notably inferior to Stairway to Heaven ripped by XLD. The differences are not subtle, and furthermore they remain consistent regardless of the orchestra/conductor/hall the 9th was recorded in.
Specifically, Page's guitar, and Plant's vocals, are far more present in the XLD version, while being totally absent from the dbpoweramp rip.
In short, XLD is markedly and objectively superior.
My finding will be presented in an upcoming issue of Stereophile. (John Atkinson's measurements revealed real & substantial differences between the two ripped files.)