You can purchase a wired sound system and use a multichannel wireless audio transmitter (easy to find at best buy or amazon). You can make any wired speaker setup wireless without losing the quality you would get with a bluetooth setup.
Here's one, but this won't work with passive speakers:
https://www.amazon.ca/Wireless-Transmitter-Receiver-Subwoofers-Surround/dp/B00SJ49ZJQ
You can still use an external power source with the transmitter as well... it's probably your best wireless bet for a good system without losing much quality.