The NAS is a Seagate Central.. I know relatively cheap but has worked well for me over the last 3 years to deliver audio files.
So maybe it does not fit your "real" definition of a NAS, but it has reliably done the job for me.
It is light and can be powered up at another location if necessary ( that has mains and WiFi , maybe at another persons home).
I have only taken the NAS / iPad and speakers few times to another location but it is a good option to have.
Have two of these NAS. One is only used as a backup.
Wireless and Bluetooth mentioned because the audio files are delivered to the iPad via wireless the the iPad communicates with the speakers via Bluetooth.
Yes the PC and iPad can use Bluetooth and wireless but the iPad is more portable than the PC ( don't have a laptop PC ).
Only hardware that needs to be on it the Cable modem/router, the NAS, the iPad and the UE MegaBoom speakers.
The modem / router WiFi covers all of my indoor and outdoor areas.
Backyard... the area at the back of a house that has grass etc...think in the USA its called maybe a back garden..?
Other option I have is to just use a mobile phone and just use Bluetooth between the phone and speaker. Limitation here is
amount of data I can store on the phone.
Thanks