Typical atmos top speakers are limited in their frequency response. By measuring the ground speakers you will just make a copy of them, including all room reflections. Your top speakers will sound identical as your L+R, but just above you (or where they were positioned relatively to your head at the time you did the PRIR measurements). In terms of homogeneous sound signature of all the front/surround/top/rear/side/wide speakers, such a virtual multichannel system can even sound better then a real speaker system ever can (based on my personal experience with the A8).
To your second question: Absolutely yes !!!! It is an exact copy of my large front speakers - and the resulting virtual multichannel system is phenomenal ! Front steering of the L+R copy of my speakers, positioning of instruments in the room and overall impact is simply a perfect copy when listening to stereo music (!).
What I have copied are my large JMlab Focal Nova Utopia BE speakers, currently installed in my living room (with no room treatment, but at least some bass correction done with a Lexicon MC-12 HD EQ V1.25 with it's Room EQ in automatic mode and manual correction of the EQ parameters):
In the virtual multichannel system and the A16, I'm listening to a 9.1.6ch system build with 16 of those speakers - performance of movies is simply unbelievable - center, side, rear, top - you name it, do sound exactly as if I have those speakers around me - more then a metric ton of speakers
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But there is an important note: It seems (at least for my ears) that variations of the microphone placement in your ear of the new A16 microphones has a bigger influence then the A8 microphone placement had. I will cover my experience in regards of optimal A16 microphone placement in a separate posting - and how I was able to make an exact copy of my front speakers with the A16. I needed to do some testing with different microphone positions and orientations to get an optimal PRIR. With my current A16 PRIR - and after doing a proper manSPK HPEQ by comparing the real stereo speakers with the virtual L+R channels - Classical, Jazz and Pop music in stereo simply sound identical with my HD800, as if I am playing the music over my speakers.
I've uploaded my PRIR and HPEQ file to the shared A16 folder on Google drive. Please feel free to try it out, but be not disappointed if it's just mediocre to you - you will most likely not have similar ear shapes then I do, so final result will vary. You should do at least a manLOUD HPEQ with my PRIR loaded and your own personal HPEQ of your headphones. See my footer with the link to Google drive if you are interested.