I`ve also had problems getting this to work. Only now have i got it to work with the standard Rio manager and i don;t know what iv`e done different to get it working. I don`t think you have to merge the rioplay with the original receiver.arf file(unless you use HPNA). Try the rioplay.arf as is.
Mercury, i think, was some internal SonicBlue name for the project. I think mercury.arf is the same as the original receiver.arf you get with the Rio manager software.

bill