Start with the brand new presets and listen for cabs that sound like "you" or fit well in your band mix. You will see the term "Rabbit Hole" thrown around a lot when it comes to IRs and it is an apt descriptor. There are a ton of killer sounds in the stock IRs and they have been dialed in by people who know what they're doing. You just spent a sizeable amount of money on this device and it comes loaded with a ton of cabs. Take the time to audition them, play with the parameters, especially the proximity effects as they really add the tube amp "feel", and dial in your definition of great tone. The stereo blend is wonderful tool as well, so take advantage of it. I personally love the blend of the Fractal Greenback cab (Prox 4.15) mixed with the Virbolux 3X10 (Prox 1.15). Gives me good low end chunk while maintaining the high end sizzle you get when pushing an amp into breakup territory. I have never purchased any third party IRs and at this point I don't plan to.