I would not put any computer within several feet of a subwoofer. Period.
You might have other options:
1) If your house is wired for cable TV, you can try using MOCA to connect it to your network.
2) If your NAS is primarily used for serving media and you don't need maximum network performance, then you can consider setting up a WiFi bridge and connect your NAS that way. FreeNAS itself does not support connection via WiFi, but a bridge will be OK as long as you have reliable wireless.
You will need to learn a few things about networking in order to set up either solution, but they are both viable options.