Battery for connectivity and control.
Simultaneous wireless is the 7X's headline feature
Running 2.4GHz and Bluetooth at the same time means you can stay connected to your console or PC while taking a phone call or listening to music from a second device, without swapping connections mid-session. The Nova 5X can do either connection type, just not both together.
Presets versus manual tuning
The Nova 5X leans on 100-plus presets built for specific games, so you pick a preset and you're done. The Nova 7X's Nova Acoustic System with a 10-band parametric EQ through Sonar software is built for players who want to dial in their own sound rather than accept a preset.
Battery is the real cost of the extra features
Running dual wireless and a more capable acoustic system draws more power, which is why the 7X's battery sits well below the 5X's. If a long session without a charge matters more to you than dual connectivity, that's the deciding factor, not the audio system. For layout ideas on keeping a headset charging cable out of the way, the OSRS setup hub covers basic desk cable routing.