Are you doing this on Windows (your given directory path isn't in the canonical Windows form, since it uses slashes rather than backslashes)? If Windows, which level? Windows 10?
Apparently your uninstallation method left behind some settings (not uncommon; it's hard to find everything). I think your left-behind information is the "open with" association of your file type, eg, .flac (or .ape or ...). I usually can change the default "open with" association by opening Windows File Explorer, navigating to a directory containing a file with the filetype I want to change, right-clicking on such a file and choosing Properties: There I will see "opens with" and a Change button. Here I can make a change. The result should apply to all files with the given filetype.
In Windows 10, you can get the same result by right-clicking on the Taskbar, choosing Settings, searching for "default program," clicking on 'select a default app for each type of file' and scrolling down to the intended filetype. If you click on the current default, you should be able to make a change; in fact, you should see JRiver MC as one of the offered possibilities.
