If the router in is an actual Cisco router running some iteration of IOS, its not likely and ideal router for home use. The cost of those devices are far beyond throughput and the ability to support a vast range of protocol and service and an endless level of configuration flexibility. For most typical home networking needs, they will be outperformed by devices that are geared for the average home user. I work on their ISR, ASR, CSR, Nexus, and Catalyst series throughout the day and except for the VM iterations, I wouldn't run any of them at home. Even with the VM iteration, it simply has features I have little use for at home.
They did have the small business line with Linksys during their ownership, but that was no more than in name. Better products were to be had by other vendors at that tier.
WiFi, even a decent unit, will have a large number of factors affecting performance. With the right set of tools, you can resolve many of the issues but some are not feasible to overcome without significant cost. Wired Ethernet will nearly always have a step up over wireless in nearly every scenario. Not always an option, but creating a test run is at least the gold standard. If there is a perceived sound quality difference, my best guess is that processors are working on error correction via TCP that address packet errors over the WiFi network. While all the data comes through, some latency through player may be created of no TCP offload processor exists that handles TCP error correction.
The Bluesound Node 2 is basically a variation of a Rasberry Pi3 like IOT board with some customized options. You're really paying for the software development over hardware. Its best use might be a transport device, but I couldn't say if it has a jitter prone output.