Not my work! Original topic here: http://steamcommunity.com/app/224920/discussions/0/1290691308592335700/?tscn=1517051552

I copypasted that guide here in case it will be deleted or Steam will not be available.
Basically it uses free (unlike xmapper and analogues) Japanese program Xinput Plus to remap deathzones and buttons of Xbox gamepad.

~~~~~~~~

Part one: XInput to DInput translation

First of all, head to this link:
https://sites.google.com/site/0dd14lab/xinput-plus
And click on the first link

XInput Plus VerX.XX.X

I know the site is in Japanese, but don't worry, you just need it do get the program.

Then, exctract the zipfile to somewhere convenient and run the
XinputPlus.exe
as Admin.

You will be presented with this screen:
http://prntscr.com/fdsma2

Click on Select (red arrow) and find your kain2.exe file in:
X:\path\Steam\steamapps\common\Legacy of Kain Soul Reaver\
as seen on the image:
http://prntscr.com/fdsnis

On the KeyAssign tab mimic the image and check the DPAD: Only 4 Directions checkbox.
http://prntscr.com/fdt9ea

On the Sticks TAB, you can correct the deadzone issue most ppl complain, just mimic the image and later you can go back here and tweak it further if needed.
Don't bother fixing right stick as it is unusable.
http://prntscr.com/fdzfsv

Skip: Triggers, Buttons, Vibration TABS and head to DirecIinput TAB.

In DirectInput tab, set everything as in the image and click the Customize Button (red arrow).
http://prntscr.com/fdspsg


In the DirectIput Key Assign window we will translate the Xinput Calls to Dinput ones.
Just mimic whats in the pictures. I used an old Dinput controller to get reference to do this.
http://prntscr.com/fdssei
*for some reason unknown Back and Start gets reversed, not to worry.

Next head to Setting TAB and follow the images:
http://prntscr.com/fdsw3j
http://prntscr.com/fdsw9k
http://prntscr.com/fdswgz


Hit Apply at the bottom:
http://prntscr.com/fdsxch

You should see this message:
http://prntscr.com/fdsxow

Now, click in TOTAL TEST:
http://prntscr.com/fdsy7m

Make sure all keys are working and then you may quit the app.


Part Two: In-Game Setup

Start the game.

You will be presented with the next image:
http://prntscr.com/fdszl5

Fill up your desired configurations and click OK.

IMPORTANT: You should hear a BEEP, meaning that XinputPlus had Loaded.

At the main menu, choose OPTIONS, CONTROL KEYBOARD and set it to CONTROL GAMEPAD, then head to GAMEPAD CONFIGURATION, and map them as:
http://prntscr.com/fdt1lb
http://prntscr.com/fdt82p

This way it should be as if it was played on ths PS1 version, except for the glyph menu that will be at the start instead of select.

If you are still unable to play double check the tutorial.