Since I do not use the flasher to put the device in host mode, I dont know if that is what is blocking you. Try this:
Use the flasher to put the 770 in peripheral mode (normal mode)
Issue the host command as root (note the device does not appear to be in host mode)
check dmesg, your device should be listed
mount the drive or whatever
when you are done issue the peripheral command to put back in peripheral mode

I just use it to access a external USB hard drive and it works great. I have always entered USB-host mode by using the terminal.