Below is the setup process for the ShakeKit, ShakeKit Plus and ShakeBox Elite.
The ShakeKit, ShakeKit Plus and ShakeBox Elite have all been discontinued. Sim Racing Studio now offers the U-Shake6 which can be purchased here. If parts or accessories are needed for your ShakeKit, go here to visit our store page. If ShakeKit troubleshooting is needed, please follow the link here.
ShakeKit, ShakeKit Plus and ShakeBox Elite Setup:
1) Connect the ShakeKit box to the Power Supply Unit (PSU) and plug the PSU into a wall socket.
2) Connect the ShakeKit box to your PC via the USB cable.
3) Place the ShakeSeat pad on your racing seat with the Sim Racing Studio logo placed near your left knee.
4) Turn on the ShakeKit by pressing the power button on the front of the ShakeKit Box
5) In Windows 10, open Change system sounds by searching for "sounds" in the Windows Search Bar. 
You can also access the Sound options by going to Settings > System > Sound > and in the Related Settings section select Sound Control Panel and skip to step #7.
If you have Windows 11, go to SOUNDS SETTINGS and select MORE SOUND SETTINGS.
6) Once you select Change system sounds, a window will open called Sound. Select the Playback tab at the top left of the window.
7) Next, select the Speakers USB Sound Device
IMPORTANT: Please make sure the Speakers USB Sound Device is not the Default Device for Windows as shown in the image above. If the USB Sound Device is the Default Device, all PC and Game sound will come out from Shakers in the ShakeKit.
If the USB Sound Device is listed as Default Device, select your PC default speakers in the window, right click on the selection, and choose Set as Default Device. You can also select your PC default speakers and click the Set Default button at the bottom of the window. This will make sure your PC and Game sound still comes out from your PC speakers and not the Shakers in the ShakeKit.
If the USB Sound Device is also listed as the Default Communication Device, do the same as above and select the Set as Default Communication Device for your PC microphone or gaming headset.
Once the USB Sound Device is no longer the Default Device, it should appears as the image below.
8) Now select the Configure button in the lower left of the window.
9) A Speaker Setup window will appear. In the Audio channels box, select 5.1 Surround and click on the Next button in the lower right.
10) Ensure all the Optional speakers have check marks next to them so they are active. Note: The window will likely show Side pair (SL and SR) instead of Rear pair. This is normal and has no impact on the ShakeKit with Sim Racing Studio. Click the Next button to continue.
11) Under Full-range speakers, make sure both Front left and right and Surround speakers have check marks next to them so they are active. Click the Next button to continue.
12) Click the Finish button.
13) This will return you to the Sound window. Make sure that Speakers USB Sound Device is still selected and then click the Properties button in the lower right.
14) Once the Speakers Properties window opens, select the Levels tab at the top.
15) In Levels, set the Speakers volume slider to 90.
16) Then click on the Advanced tab at the top and make sure the Default Format is set to 16 bit, 48000 Hz (DVD Quality).
17) Now click the OK button at the bottom of the Speakers Properties window.
18) To finalize setup in Windows, click the OK button at the bottom to close the Sound window.
19) Now open Sim Racing Studio and go to the SETUP > License page
20) Enter the license key you received by email into the Key field and click the Activate button. Note: If you already have an active Motion and Shakers license from your motion platform purchase, there is no need to enter a second license key.
If you do not have your license key available, click on the Forgot my license button and enter your email address you utilized to purchase the ShakeKit and click Confirm. Then check your email, including your spam folder, for the license.
21) Once your license is activated, go to the SETUP > HARDWARE page
22) In the SHAKERS section, click the Soundcard drop-down menu and select Speakers (USB Sound Device) and in the Profile select SRS ShakeKit or SRS Shakebox Elite.
If you have a ShakeKit Elite or an extra Buttkicker Gamer 2 connected to the ShakeKit, select SRS Shakebox Elite + Sub + Center in the Profile drop-down menu.
23) IMPORTANT: When finished, click the SAVE button in the upper right inside the PROFILE IN USE box to save the settings in Sim Racing Studio.
24) To verify the ShakeKit is setup correctly, click on the Test buttons next to the FL (Front Left), FR (Front Right), RL (Rear Left), and RR (Rear Right) Shaker sliders. You should hear a vibration from each of the respective shakers tested. If there is no vibration coming from any of the Shakers when selecting the Test button, please click here for troubleshooting guidance.
25) To check if your game is setup and ready for the ShakeKit, go to GAMES and select PC or Console. Scroll to the game you are about to play and check to see if Ready to play is shown in the STATUS column. If Ready to play is not displayed, please check the guidance here. 
26) Your ShakeKit and ShakeKit Elite are now setup and ready to use! Have fun!
Additional Resources:
For troubleshooting your ShakeKit, follow the link here.
For guidance on tuning your ShakeKit, please refer to the Shake Tuning Guide here.
Below is an older setup guide video (please disregard the drivers installation as they are no longer required) that will show many of the steps above: