The answer is found in Karate Kid II:
Remember, best block, no be there.
You cannot break a device that you don't have, and you cannot steal something of which you don't know the location. You cannot decrypt a no-sucks encryption without knowing the key. You cannot coerce someone telling you the key if the person doesn't know the key. You cannot restore a split secret if you don't have all the parts (or a certain number, at least).
So the first obvious defense is to make the location of the devices/disks unknown and the disks physically inaccessible. Make sure it is unfeasible to get all parts.
Rent a couple of bank safes, do not tell anyone where. Put one disk with one shared-secret part in each. Depending on your paranoia level, you might even have two or three trusted people independently rent safes (and possibly more than you need), and give one or several of them a share of the secret (without knowing where they've rented the safes yourself, or in which one they'll place the disk).
Use a random encryption key long enough so you cannot remember it, and have another trusted person keep it. Or, have two people store half of the key each. Could give one half to your attorney in a sealed envelope like in a 1970s spy movie. Or put it in yet a different safe, hide it on a cemetary, whatever. Protected storage on a smartphone would be an option. Both Apple and Samsung offer protected storage and will wipe memory after so and so many failures if you tell the phone to do that. Give your lawyer that phone.
Adversaries might break the safe in your home or your office. But few, very few, adversaries can break into a bank safe, let alone break into several of them either at the same time or without being noticed. As soon as one bank safe is broken into, you will be informed. So they must be really, really, really, powerful to pull that off.
If the possibility of your adversary breaking into 3 or 4 banks simultaneously and figuring out the encryption key is a realistic concern, please stop reading now, buy some rope, and hang yourself. Or, just give them your secret.
An adversary who doesn't have all split-secret devices cannot use the data even if he has some of them (well, it depends on the scheme you use, could need N-1 or N-2, or N/2). An adversary who doesn't know the encryption key has nothing but rubbish in his hands, even if he has all the parts. So... make sure that cannot happen.
The easiest, most obvious split-secret scheme that you can use without special tools is RAID-0 (or RAID-5 if you want to trade the small risk of the adversary finding N-1 disks against the risk of losing one by accident) in combination with any kind of does-not-totally-suck file-based encryption. Anything that does any kind of block chaining and uses a no-joke algorithm. Which is pretty much what every standard archive tool like 7z or such does. If you have reason to believe your adversary can conceivably break the encryption that 7z uses, then see above, buy rope and hang yourself. Nobody can help you.
As an alternative if RAID sounds too scary to you (never heard of?), you could add some random data to an (encrypted) archive (doesn't matter what, just to guarantee a minimum archive size to start with), then add all your secret data, and finally select the "split archive to..." option to generate several small sub-archives. All but the first part (which contains only random noise) are worthless without all of the preceding parts. Put one on each disk, done. You can even add some redundancy by hand if you like, in case one disk is lost. Only need to create more segments and be sure each is on at least two disks.
Or, create an encrypted archive, split in two, add the parts in reverse order to another encrypted archive which you then split in N parts (don't need random noise then, cannot decode any part, including the first, without the other parts).
If an adversary doesn't have all the disks, then whatever he has... it's completely worthless. There's no way he will decrypt the archive, or part of it, even if he knows the decryption key.
If the paranoia level is at its top, you could complement the whole thing by further adding filesystem-level encryption. But that's actually kinda silly.
