Beware of buying an SSD that is running USB 3.0. it may be incompatible with your system if it's running USB 2.0.
I initially bought a Samsung 2TB SSD. It was not compatible with with my Marantz or Cambridge units. A NAS is overkill in my opinion just adds cost and setup complexity. I ended up getting an external 5TB HDD that uses USB 2.0 and connect that directly to my Cambridge CXN V2. Search and playback are very quick. No delay. Back up is done via my laptop using the Samsung SSD as the backup.