Help with nandroid backup

[Boxfreind]

I have rooted my V10 H900 and want to do a full backup of the phone before I attempt to unlock the bootloader, install TWRP, and then install a custom ROM. I have installed Titanium Backup...what a piece of garbage, It's like the UI was written by a 5 year old with ADD. I decided to try Helium instead but it throws a SuperUser error "non zero result 1" (I am using SuperSU and BusyBox). I have checked the permissions in SuperSU and it looks right. Does anyone know what to do to get past this? Is there a better app/method to backup my phone?
Also i would love some input into which recovery to use as well as which ROM's work well with the V10 H900.

 

[krissebesta]

There are no custom ROMs for the AT&T V10. The bootloader is locked and no one has been able to unlock it yet. Only the European version and the T-Mobile version are allowed to unlock the bootloader. I gained root for Lollipop and then used the FlashFire app to do a NAND backup. There is not a rooted version of Marshmallow for this phone yet.