One thing I forgot in my review of the K17 was the dedicated FiiO DSP application (as I had presumed it was only on Windows and I mostly use a Mac). But I noticed there is a FiiO DSP App in the Mac App Store and I thought I would give it a go today (and also fired up my Windows Laptop to compare it with the windows version) and both are mostly the same - the Windows one has a RTA analyzer which is very cool but I do think this is the "icing on the cake" as far as the K17 is concerned especially for those who like to tinker with settings.
The normal Windows editing a specific filter:
When running the RTA:
And here is the MacOS version after editing a filter:
And the FiiO Control mobile apps also can see and edit the various filters - but do not have access to all the various tweak.
I know this app was originally for the K19 but I think it is a nice addition to the FiiO Control App "PEQ editing" capability.
The normal Windows editing a specific filter:

When running the RTA:

And here is the MacOS version after editing a filter:

And the FiiO Control mobile apps also can see and edit the various filters - but do not have access to all the various tweak.
I know this app was originally for the K19 but I think it is a nice addition to the FiiO Control App "PEQ editing" capability.