Is the sensitivity the same on the omni as the 8's? If so, I'd suggest running the exact same gain on all three channels, which will make the matrix decoding simpler and easier to understand.
On the zillion possibilites, I'd suggest trying some ambisonic software. What you have with that mic when matrixing all three capsules is horizontal only ambisonics. Your mic feeds, assuming all the caps have equal sensitivity and you orient the mic M/S, are straight Ambisonic B-format without the Z component for height (W,X,Y). There are many different apps and a good deal of them free, developed by university research types. Many allow you to simply plug the three files in and then manipulate mic patterns and angles on the screen while you listen. So you can dial in Blumlein, play with the angle, or widen the pattern to hyper or try 130 degree cards or whatever, all while listening. Makes it much easier to mess with and far less intimidating than doing the raw matrixing on a mixer or in your daw. Plus I've found no better learning tool for 'closing the mental loop' between the reality of what you are hearing out of the speakers and the abstraction of mic patterns, angles, configs.
Making sure the gains are exactly equal for each channel (assuming the sensitivitys are equal between capsules) is critical to having that work right though. When I was using my Oade CM R-44 for the Tetramic, I'd balance the input gains exaclty with a signal generator and a multimeter before recording.
Hit me up for details if interested.