[General Topics] Elements1984:
I have just checked the XML file you posted here in the first page of this thread, I checked it looking for a keyword such as "Hz" (which translates to Hertz) but I found nothing related to what you were looking for, so this lets me think that the tonal balance is not controlled within this file.

In my understanding, this file tells various sound hardware components how to behave in various scenarios and the values it should have. Equalising and sound processing is most likely done somewhere else, and this is where sound processing gets divided into two types :

1 - Driver level processing

2- App level processing

To go into more details, here is how I see it done:

1 - Driver level processing is when you have a driver installed within your rom that takes care of processing ALL the sounds, such as SoundFX in CM or Viper for those who want a much better control over their sound. Basically, whichever software will be used is going to be an interface (UI) allowing you to adjust the driver which will act as a sound processor for all the system sounds and all these will be tuned according to the desired settings assigned when setting up this. This will affect everything, from mp3 listening to watching videos to even your alarm and the FM radio.

2 - App Level processing is when your sound is processed within the app you're using, such as when you use the mp3 music player apk that has an incorporated sound adjustment suite and you adjust the equalizer in there, this will not affect the other system sounds, meaning that other apps will not benefit from this tonal adjustment you made within the mp3 player app.

Following these two processing types, the approach to modify through file system editing should be different.

For the App level processing, I believe this should be done using the included equalizer rather than trying to unzip the apk and edit the values.

For the Driver level processing, this can be interesting to consider digging into if you wish to manually assign values to the driver, although this would be less practical since you already have a user interface that makes things much faster and easier.

I remember that with my Galaxy s3, I had a kernel which allowed me to set an equalizer to the master sounds (basically it's what you're looking to achive). I am not sure if it interacted with a system file or if that was kernel based. You can try the Boeffla Kernel for the S5 with an app such as TricksterMod or something compatible with this kernel. Hopefully it will provide the possibility to tune your sound as well as provide some interesting other features such as double tap to wake (knock knock feature from the LG G2 and successors).

Can you tell me what problems you encountered when installing Viper? Are you sure you have all the pre-requisites installed? (such as busybox)

Did you disable other sound improvements before trying to install it? If the rom is Marshmallow based, Busybox is acting weird and it is a bit tricky to get Viper running, but you shouldn't encounter problems under lollipop.

Give me back some information and I will try to help you as much as I can ;)

Edit :

Here is a link to the boeffla kernel features description for the s3 and s5, head to the section "5.4 Equalizer" and read that description, it's possibly what you need and you don't even need Viper.

http://www.boeffla-kernel.de/index.php/kernel-settings

To download the kernel and the app for the user interface, here is the link:

http://www.boeffla-kernel.de/