Readynas 214

bonnie5689 is clearly unfamiliar with the file system on a ReadyNAS and may be trying to sell you something.

I know of no other brand of NAS that supports BTRFS on MDADM RAID as is used by OS6.

Neither of the recovery products mentioned do either.

If you want to put your drives in another NAS and just "keep on trucking", then a used ReadyNAS running OS6 is what you need.  Any model with at least 4 bays (unless you've only used 2) will do, including a legacy unit converted to OS6.  Which you chose depends a lot on whether you want to continue using it as a primary NAS, a backup to another brand, or not at all.  Unless it's "not at all", I recommend you avoid the 104, as it is quite limited.  Note that if you do go with a legacy unit, you'll need the caddies -- yours will not fit the older units.  Many are sold without them, unfortunately.

Recovery with a generic LINUX system with both MDADM and BTRFS installed is possible, if you have the skills, as long as what happened to your NAS didn't damage the volume in the process.  The only recovery software I know of that supports the OS6 file format is ReclaiMe, which is somewhat expensive but does have a free mode that can tell you whether or not it will work before you purchase.  But it will often also recover most files from a damaged volume.  In both cases, you'll need a way to mount at least 3 of the drives (all 4 is best) simultaneously to a PC.