Hello @Tdot16
It's actually worse than them just being on the same "channel" – if the JBL system was using WiFi to carry the audio, they'd be able to share that spectrum just fine. But, the JBL system is using the same spectrum (range of frequencies) in a non-WiFi compatible way. So, to the WiFi system it looks like interference, which makes sharing that spectrum much less effective. This is frustrating because both systems are following the rules for that spectrum.
So, it turns out there is a reason both systems "like" that spectrum. Those rules allow for a higher transmit power in that part of the 5GHz band, which increases range and throughput. The other parts of the 5GHz band are subject to other rules that make using it more challenging. There is a lower channel WiFi could use, but it would have to reduce the transmit power (and to be clear, we're already talking about quite low transmit power already). There's also a range of channels in the middle of the band, but they are subject to "DFS" rules, which would require coordinating which channels can and can't be used based on the physical location of the system and what large scale weather radars are in operation in that area. So, Google/Nest WiFi (and JBL) pick the upper part of the 5GHz band to avoid all of these issues. That's why you can't change the channel on either one of these systems.
You mentioned it would be difficult to move our primary Nest WiFi Router unit. But, unfortunately, there are really only two options: move it (preferably to another room, but if you can get it 20-30 feet away from the soundbar, that may be sufficient) or give up one of the two products. Just be aware that other 5GHz WiFi solutions may be subject to the same constraints. There are products that let you select a DFS channel, but if you pick something that is used by your local weather radar, it may not work well. Alternatively, a wired speaker system will avoid the issue as well. I know both of these solutions require running some kind of wire (either a longer Ethernet cable to get the Nest WiFi Router farther from the cable modem or running speaker wires), but limited spectrum means doing everything without wires is going to run into issues like this.
