I don't understand what you are trying to explain.To put it in a nutshell, what is the point of buying a Receiver that has 9.1, 11.1, 14.1 or anything higher when it is only utilising a 7.1 source to create it?
If you are interested in experience Dolby Atmos, how many speaker do you need (or want) to feed ? Only this question can determine the receiver model you are going to choose. If you consider that a 7.1 receiver is ok for your using, so be it.
According to Wikipedia : Dolby Atmos home theaters can be built upon conventional 5.1 and 7.1 layouts. For Dolby Atmos, the nomenclature differs slightly by an additional number at the end, that represents the number of overhead or Dolby Atmos enabled speakers: a 7.1.4 Dolby Atmos system is a conventional 7.1 layout with four overhead or Dolby Atmos enabled speakers.[20][21] The simplest Dolby Atmos setup is 3.1.2,[22] the most complex one is 24.1.10.