The Rio IP and engineers went to Sigmatel [1], who essentially turned the firmware for the Rio Karma into a reference firmware for their MP3 player SoCs. The Trekstor Vibez [2] was probably the most well-known player that used that platform.

By the way, the Karma firmware was really ahead of other players of the time, supporting perfect gapless playback, Vorbis and FLAC support, and on the fly playlist editing. The iPod never got on the fly playlist editing, which I really missed when I moved over to using one from a Karma.

[1] http://www.theregister.co.uk/2005/07/27/sigmatel_rio_deal/ [2] https://en.wikipedia.org/wiki/TrekStor_Vibez