AllTrack and SoundExchange are different organizations that collect two completely separate royalty streams for music creators and artists.
AllTrack, collects performance royalties for compositions (the actual notes and lyrics of a song, independent of any recording) for almost any form of music use – streaming, radio (satellite/FM/AM), television, live performances, and for uses of music by all types of physical businesses (restaurants, bars, nightclubs, hotels, etc.). AllTrack strictly represents creators (songwriters, composers, producers) and publishers, who are the owners of compositions.
SoundExchange, on the other hand, primarily collects royalties for the non-interactive streaming of sound recordings on digital platforms (i.e. Pandora, Internet Radio, SiriusXM). SoundExchange strictly represents artists and labels, who are the owners of sound recordings.
An independent creator that both writes and records a song is legally the owner of the composition AND the sound recording. Therefore, this type of creator is entitled to royalties for the the composition AND the sound recording, and should therefore signup for both AllTrack and SoundExchange to maximize their royalties.