Are you checking your gain structure before decapitator? And the obvious one's like are you pushing it too hard through decapitator (drive)? I do find that even without the punish button, if you overdo the signal or drive, it can get quite gritty. What other saturation do you have?
Before the course I only had soundtoys and Cubase stock 'datube', and even then didn't really understand them. I now have slate and what a difference. For $15 per month it has made a huge difference. Then just follow the MMWA channel strip. Seriously, it works. I am now starting on UAD but that stuff doesn't come cheap. Again though, it does work.
As for other systems, this is one of my pet hates. You try to get the optimum monitoring environment, or buy really expensive monitoring headphones and yet still the true test is when you get in the car or on your phone with 'regular' earphones etc. I did think or wiring a car stereo up in the studio, but even then it wouldn't work because of the room! Think for now this is one we have to live with. You did say though that it sounds great on everything you had tried except the dive bar. In the same way we use reference tracks in the studio, what do other tracks sound like in the same venue? Is it the venue system generally, or the mix when played on lower quality systems?
Again, hope it helps. Because the question was around saturation, I have jumped in on it being a saturation issue. Remember, it may not be. I would definitely check gain structure too. Regardless of how good/safe it sounds when monitoring, unless you want the overdriven effect, just watch the needle on the saturation and keep it out of the red. Even if that means having 2 or more instances of decapitator after each other (probably using a different mode like A and then E). That is if you are just trying to warm things up, not burn them for effect.. after all, some people like black toast!