Did you ever get anything working?
If you just want all of your speakers playing, not true 5/7.1 you can use software like Voicemeter to expand 2 channel audio. Some audio devices have this option in their settings too.
I don't recommend trying to use this test as a means to play AC:Odyssey, if only because in around a month and a half it'll disappear anyway, and if you care about the game instead of the service, you probably want it for longer than that (especially considering the continuing support the game's been getting, or the inability to get DLCs in the Project Stream version for obvious reasons).
You could wait for Project Stream to launch, at which point I assume AC:Odyssey will be one of its launch titles.
As far as I know, there's no way to bypass the connection test. You can follow the tips on the page itself. To verify if the issue is Project Stream-specific (or if your connection actually isn't strong enough), try to run a https://fast.com or https://speedtest.net with US unblock and similar network conditions - if you get radically different results, might be time to consider ISP throttle (or US unblock, for that matter). If nothing else, make sure you're actually getting 100mbps down.
Express is definitely not the fatest, or most secure either. The latency is fine, that's more of an issue with your local infrastructure and ISP's peering. When using nearby VyprVPN servers I only get a couple extra milliseconds. Speedofme also tends have accuracy issues at times.
I get only latency in the 50-60s connecting all the way to central america.