My rule of thumb is to never spend less than 2x or more on an upgrade or you are likely to just make a horizontal move. I don’t think I have ever been disappointed following this rule. However, I do a lot of research to make sure the sonic characteristics are consistent with my values… level of detail, sonic balance…. Etc.
Given the modest cost of Bluesound, I would recommend a new or used Aurender… the most basic is at least a level or two of performance above Bluesound.