If you want the Fractal to sound like your amps running through a live guitar cab in the room with you, run a Fractal amp model into a good power amp and a live guitar cab in the room with you. No modeler can magically transform studio monitors or any other speaker into a cranked up guitar cab. When you run direct with the Fractal using a cab block you're recreating the signal from a mic on a guitar cab in another room, monitored through whatever speakers you're using. This is a much different sound than a live guitar cab in the room with you and many people mistakenly blame the modeler for the different monitoring paradigm. If you've ever recorded real amps in a real studio you know the sound you experience in the live room with the actual cab is much different than the signal from the mic on that cab through the monitors in the control room.
Acoustic treatment is crucially important for accuracy but I wouldn't bother with it if you aren't recording, dialing in tones for live use, or trying to match recorded album tones.