Did you try Poweramps Music FX function? From your pictures, it looks to me like the Hifi settings are a separate equalizer/audio settings app, rather than purely integrated into the player. In a similar way, I can use Sonys ClearAudio and ClearBass etc etc on my Z3c with Poweramp if I choose (although I choose not to).
If it still doesn't work, I suspect this would force me to wait until a fix comes. Poweramp is still the only player I've found that can do album/list shuffle (with songs still in order), besides having really robust and stable functionality in general, even if its not the best sounding. If the stock player can do that, interest remains... can it at least deal with music on the SD card? Still stuns me that so many stock players can't even do that.