Some good progress! After reviewing some similar issues on Linux Mint's forums, I have a currently working solution.

First off - Not sure if the full re-install would've been necessary at this point and obviously I can't revert now.

The following are installed (not sure if all are required; will continue testing and update thread as time goes on)
- intel-microcode
- firmware-linux-free
- firmware-misc-nonfree

Even though the resolution wouldn't show up in the 'Displays' menu, xrandr was still able to add and set the resolution but I needed to use the reduced blanking option with the cvt tool.

$ cvt -r 1920 1090
# 1920x1080 59.93 Hz (CVT 2.07M9-R) hsync: 66.59 kHz; pclk: 138.50 MHz
Modeline "1920x1080R"  138.50  1920 1968 2000 2080  1080 1083 1088 1111 +hsync -vsync

The output from cvt is then used to create a new mode with xrandr.

$ xrandr --newmode "1920x1080R" 138.50 1920 1968 2000 2080 1080 1083 1088 1111 +hsync -vsync
$ xrandr --addmode DP-1-1 1920x1080R
$ xrandr --addmode DP-1-2 1920x1080R
$ xrandr --output DP-1-1 --mode 1920x1080R
$ xrandr --output DP-1-2 --mode 1920x1080R

After that I had the right resolution on both monitors and no visible flickering for the past 5 minutes!! Now upon restart the screens revert back to 1920x1080 at 60Hz and the flickering is back but re-running the above commands all was good again. Afterwards the resolution shows up in the displays menu as well.

I'll experiment with scripting this so that it auto applies on boot up but if there are any better ways to handle this, please let me know!

I wish I could move solely to alsa but try as I may, simply can't figure out how to record streams with solely alsa on this machine....

I'm certainly hoping for the same thing! pardon my ignorance but I thought that the something about the I.MX6 platform was specific to it and required special consideration? Perhaps I'll just try install the Debian image and then switching the sources over to devuan to see what happens.

I've not experimented with my dells yet but my Toshiba Satellite was simply as easy as loading my custom keys, building a stub-load kernel, signing it, and then enabling secure boot in the bios. Will be interested in what you find out with your Dells though.

Even saw some Dells the other day where CSM isn't an option within the firmware! Figured at some point everyone would move over from CSM/Legacy just wasn't sure when.

Czeekaj - I unfortunately don't have the ability to build my own chips, PCB's, FPGA's, and what not so I'm sort of stuck trusting hardware vendors at a certain point. Secure boot at least makes the bar for high jacking my system 'a little bit' more difficult!

Not going to say there isn't an alternative but I had the same issue on a Lenovo laptop with a quadro GPU. I just gave in and installed the 418.88 driver from Nvidia and haven't had an issue since.

Good point. Didn't look at it that way but I can definitely see things going that route, sadly.

That tallying system made the head hurt...

Didn't go as badly as thought but not as promising either. :-/

What's next?

Yea... Was wondering this exact thing when reading through the options. Lots of fragmented options for non-systemd.

If Debian goes full systemd, what will this mean for Devuan?

I've wanted to use FreeIPA but haven't spent the time to go through the process. Did you happen to write up the steps and changes you made to make it work in Devuan?! I'd definitely be interested.

Man... I wonder if they need people to test that LTS branch?!