DTS versus PCM

When I choose on Apple TV settings Dolby Digital 5.1 and on Infuse the Passtrough option, I have DTS or Dolby Digital on my receiver, according to the moving sound format. If I choose your recommended settings I always have PCM on my receiver for digital sound. According to you I understand this is better but then on my 6.1 sound system I only have sound on my rear speaker on movies with DD/DTS 7.1 chanels. I understand the reason of that but I wonder if this is better then a simulation of some sounds on rear speaker with other sets, for DD/DTS 5.1 movies.