thank you for suggesting maketecheasier! i consulted this guide and was able to get a 5760x1080 wallpaper spanning across all screens! unfortunately, i still cannot get games to recognize that i am running this resolution, but i believe i could force them into running it at this point. i'm still going to try and get them to see it natively however.

i'm going to show my steps just in case someone else has this issue and stumbles upon this thread. note, i updated the steps the author of that article used for Debian 8, so some of the commands are a little different.

in a terminal become root, then:

gedit /etc/X11/xorg.conf.d/20-nvidia.conf

note: the 20-nvidia.conf should be the name of whatever you called the xorg config file, also just using gedit because its standard text editor for Debian, replace that with the name of whatever text editor you'd like.

i created a subsection under "Screen" like the author did, however changed the details to fit my configuration. i should also note that i opened nvidia-settings in the terminal and created a new file, and then deleted the old one as root, just so that it was updated with the correct settings. as if you follow the Debian wiki guide your file will have like 5 lines of code.

 SubSection     "Display"
    Depth       24
Modes "1920x1080" "1920x1080" "1920x1080" 
Virtual 5760 1080
 EndSubSection

substituting my modes for three 1920x1080 monitors, this may be changed to whatever resolution you're running. the virtual is the total value of the three monitors' width. save the file. back in the terminal again, restart your X server.

sudo /etc/init.d/gdm3 restart

substituting gdm3 for whatever you're using, in this case i'm using Gnome. back in the terminal run..

xrandr -q

to see your monitor names, etc.

run this command:

xrandr --auto --output OUT1 --mode 1920x1080 -- auto --output OUT2 --mode --right-of OUT1 --auto --output OUT3 --auto --right-of OUT2

replacing the OUT's with your monitor names. here is mine for example:

xrandr --auto --output DVI-I-1 --mode 1920x1080 --auto --output HDMI-0 --mode 1920x1080 --right-of DVI-I-1 --auto --output DVI-D-0 --mode 1920x1080 --right-of HDMI-0

open a text editor, as we need to write this into a script so that it will happen at start up automatically.

in Debian, files which are to be executed by bash need to start with

#!/bin/bash

below that just copy the command from above so your file looks like this:

#!/bin/bash
xrandr --auto --output DVI-I-1 --mode 1920x1080 --auto --output HDMI-0 --mode 1920x1080 --right-of DVI-I-1 --auto --output DVI-D-0 --mode 1920x1080 --right-of HDMI-0

save the script as whatever you would like, in this case i just copied the author of the original article and named it startxrandr. save this file to your /bin/ directory, ending with .sh so that its apparent that it is a shell script, not necessary, but it makes it easier to see. then as root run this command so that it will execute on startup.

chmod ugo+x startxandr.sh

startxandr.sh being whatever you named your file. after all of this, i was able to set wallpapers across all three screens. will update again once i have games working!