Just a rough guess...
All those fake multi-channel emulaters operate off of phase differences and other niceties that are hidden in the original signal.
MP3's, by nature, squeeze and discombobulate all kindsa stuff so as to only store the bare bones needed to convince our ears that what we're hearing is "real" music.
While our ears may think it's ok, perhaps these circuits need a bit more to work on.
Did you try DPL or neo with any other analog sources, like FM radio, phonograph or even a two channel CD?