I have this exact problem too. I'm ENG S-OFF and ARHD 9.2 installer is fine until the very last step when it goes "assert failed" and something about extracting the boot.img to /tmp/boot.img.
I tried going about it the same way I read before with CyanogenMod where I'd manually flash the boot.img in fastboot to make sure it was flashed properly or I'd just get bootloop into recovery, but it's a no-go. It flashes fine, of course, but it doesn't help one bit. I'll be damned if I'm giving up and moving to CyanogenMod again after going through all the guides and reading page up and page down of things that basically didn't help me.
Does anyone have a solution or an idea why ARHD 9.2 fails when extracting the boot.img to /tmp?
EDIT: Same issue with ARHD 7.3 btw.
EDIT2: I gave up and went to CyanogenMod 10.2. Worked the first time...