[Shield Android TV Accessories] copticwalad:
See my answer after next quote.

I finally got around to grabbing all my usb sticks and hdd's and a few devices and trying it out. I found that there is some sort of firmware limitation that allows only 2 usb storage (FDD + HDD) devices to show up. I'm not rooted yet and am still on stock ROM but may look to change that after we get marshmallow this month. Keep in mind though you can power an xbox 360 for windows wireless receiver, a logitech unifying receiver, even logitech wired gamepads along with 2 Storage drives (HDD or FDD) on a single usb port. I did try a 5400RPM usb 3.0 in NTFS drive along with a few flash drives in exFAT, NTFS, and FAT32 formats. The way I'm noticing it's behavior is you can have say 5 drives connected overall, say a 7200rpm on other main usb port, and then 5400rpm + 3 flash drives on unpowered usb hub but the Key is, the system will ONLY show you the last two plugged in. If one is removed, it should show another one (if not then you'll need to disconnect/connect) and they are all powered interestingly, even when not shown up.

Summary from my tests so far:

-Connect as many USB devices (controllers, keyboard mouse receivers, xbox 360 receivers, HDDs, FDDs) as you want through usb hubs, if you have more than two 2.5" drives I'd recommend a powered usb hub.

-All devices so far have lit up and power on as long as there's enough power

-The obvious Limitation so far, is software limits access to 2 most recently connected Storage USB Devices, this is despite being fully lit up and hard drives spinning. You can unmount them easily though in Android Settings -> Storage & Apps -> Unmount.

*This is reflected in both ES File Explorer and Android Settings

I'm going to talk about how I usually approach watching my media... so feel free to read

*I recommend to everyone to try and find alternatives to ease your lives. I'm a crazy tech enthusiast and even though I have soo many hard drives and flash drives from over the years, I've learned to simplify things and accommodate accordingly. For example PLEX is an amazing solution for watching videos over the network on this nvidia shield, and even though I do plan to eventually use Gigabit, wireless AC over 5Ghz is ridiculous on this thing and has no lag. In fact, even though I could connect my 6TB external hard drive to the unit directly, I still prefer the plex interface and ability to watch on my phone or tablet instead of my tv based on a number of factors. The other thing you could do if you don't like plex is simply use Windows network interface and Share 1 specific folder to your network that you can easily access on ES File Explorer. You can make it a little easier by assigning a specific computer in your house to 1 Local address, so the ip address never changes. For example: 192.168.1.2 could be assigned to your favorite computer, so then in ES File explorer you can save that SHARED folder as a favorite after scanning your network and then access it easily and wirelessly and not worry about flash drives etc..... Lastly don't forget about the awesome Casting abilities of the Nvidia Shield, so you can just cast your screen on your smartphone/tablet and if you have family photos on say Google Photos (released 6/2015 and highly recommended for everyone), you can cast them all on the big screen. Don't be like how I used to be and have literally over 10 drives and flash drives, each hard drive being like 500gb or 1TB and a bunch of scattered media on flash drives. Instead simplify your life and put all your media on 1 huge hard drive (ideally with RAID 1 security backup built in or offsite backup) and keep maybe one On The Go speedy flash drive, like Sandisk Extreme USB 3.0, for media you put temporarily to watch on a trip or something. Let me know if there's anything else I can do to help, but that's a summary for novices.