Can you please test out asterisk with mpg321 installed instead of mpg123. It should work unless k3b needs some of the rarely-used features of mpg123. If it works, please update the ebuilds to use virtual/mpg123.
asterisk needs some of the advanced/rarely used features of mpg123, there is a patch floating around the net to make it work with mpg321, the problem is this will pull in another dependency (sox, which is needed to convert the ouput from mpg321 to 8000Hz mono)
ok, just leave the dep as media-sound/mpg123 then, Thanks for looking into it.