Why would you root immediately without even trying any of the apps, especially UAPP? I have S7 edge, use this cable:
http://www.amazon.com/Meenova-Mobility-Cable-MicroUSB-MicroUSB/dp/B00ZYB44UW
with UAPP and everything works perfectly. I have not rooted anything.
As far as Iphone's being better... Iphones will output all audio from all apps to mojo, bypassing the built in DAC in the iphone. Androids will output all audio played through UAPP/Onkyo/hiby(dunno haven't used hiby) to mojo, bypassing the built in DAC in the android phone. However, anything else you want to play via android phone; youtube, stitcher, tune-in, bandcamp, etc, it will all be upsampled before being sent to the mojo-at least for now as no one has developed an app that can send the output from these programs directly to the mojo as well.
Also, why buy 3 phones? It would seem with a little research you could have just bought one that you knew worked instead of buying 3. just curious.