Dual booting AppleTV OS on internal drive and OSMC on external usb drive

I have few questions because I am wanting to dual boot the ATV OS (stock) along with OSMC on an external drive. I will be using the internal ATV drive for SD and the external OSMC drive for HD (720p) playback. Is this possible? Do you know of any forms among the thousands listed here on OSMC’s site? Thanks.

Do you mean an external USB hard drive or do you mean a USB stick ?
Do you have a Crystal HD card installed ? Without one, you likely will not get reliable HD playback.

Yes – you can do this.

Recommend a USB flash drive. Spinners may time out during the boot process.

I just did a test install of the latest Nov 2016 of OSMC, on an old 160GB USB HDD that can power itself from a USB port.

It works fine.

To do that, I simply used the OSMC installer, selected the latest USB install version, and followed the normal installation steps.

If you are using a modern bigger drive, you would need to have the drive connected to a powered USB Hub, or that has an external power supply, because the ATV USB port only supplies the minimum spec 0.5 amps

Using a powered hub also has the advantage of allowing more devices to be plugged in.
This is helpful if you want both wifi and a CrystalHD decoder card, since the decoder card replaces the internal wifi card.