[Galaxy S6 Edge+ Themes and Apps] galaxyYtester:
Welcome to the guide on how to enable soft keys and get the Nougat notification shade on Samsung Marshmallow ROMs

Normally you can just edit build.prop and add the line qemu.hw.mainkeys=0 to the end and soft keys will appear, this trick does not work on stock Samsung Marshmallow (but there's an easy way to enable them), here's what soft keys look like on stock rooted Marshmallow with Xposed installed (it is stock Samsung MM, looks Cyanogenmod because I installed cyanogenmod apps and did theming) :) :

First let's enable the soft keys

1. Root your device: http://xdaforums.com/s6-edge-plus/general/easy-root-s6-edge-plus-marshmallow-6-0-1-t3325477

2. Install Xposed on your device: http://xdaforums.com/xposed/unofficial-xposed-samsung-lollipop-t3180960

3. Install the Good Lock app by Samsung on your device, it's free on the Samsung store but here's an apk, if there's a newer version choose it instead: http://www.apkmirror.com/apk/samsung-electronics-co-ltd/good-lock/good-lock-24-0-11-release/

4. Download the module GravityBox [MM] from Xposed, activate and reboot

5. Open the GravityBox app, go to Navigation bar tweaks, turn on the Master switch and Enable navigation bar, reboot, soft buttons will appear

Now to disable the capacitive buttons

1. Install Root Browser

2. Navigate to system, usr, keylayout, and tap on "Generic.kl", Open as, choose text file and RB Text Editor

3. Scroll down to key 158, and put a # before the word key in the line, so it should look like this: "#key158 BACK"

4. Scroll down to key 254 and put a # before the word key in the line, so it should look like this: "#key 254 APP_SWITCH", after this save the file and exit root explorer

5. To disable the lights in the capacitive buttons, download an app called "Galaxy Button Lights" from the Play Store, in the app choose "Always off" and save

6. Reboot, after this you will have soft keys and your capacitive keys are disabled and don't light up! :D

BONUS: Android Nougat notification shade on Stock Samsung MM ROMs:

I've noticed that the Android N-ify Xposed module does work if you install Good Lock and looks the best if you enable certain settings, here's what it looks like:

How to enable it and make it look the most original:

1. Have the Good Lock app installed

2. Go to Good Lock settings and under Advanced, make sure everything is turned off (you can turn the last one on if you want to, it doesn't affect this process in any way)

3. Go to routines and edit your default routine, in theme color scroll all the way to the left until reach the pure white color, after this go 6 steps to the right, you should be in the darkest shade of gray before black

4. You can see the derived color palette in the bottom, drag the colors so they are in the order of the darkest being first, the second darkest being second, the lightest being third and the third darkest being last, save changes to the routine

6. Install the Android N-ify module from Xposed, enable it and reboot

7. Open the app, go to Status bar header and make sure these options are enabled:

Style header

Alternative QS loading method

Enlarge first row

8. Reboot, now your notification shade looks like you're running Android Nougat, I hope you found this guide helpful :)