For me, I had to learn what the tones I liked sound like on different playback systems.
What I do is A/B a track from a record I love with what I am working on. This gets you apples to apples listening on the same speakers in the same room.
The low end is the hardest in that most speakers and most rooms in general don't reproduce the lower octaves accurately.
For the low end, I recommend lots of trial and error to learn what works for your room and speakers where you create your presets.
I don't really expect to get the same tone that I get with my 6505+ and Mesa 4x12 (which is absolutely crushing) on these KRKs, just want something at LEAST comparable.
I don't know if any of you have seen it on the tone sharing part of the Fractal website, but I downloaded the FAS Modern tone which wires two heads through two cabs. This sounds absolutely crushing on the Mesa, but on my speakers, or headphones, or any other output OTHER than the Mesa, I get this crackling sound with it (possibly because these outputs are trying to handle too much frequency or something). Unfortunately, this is still my best tone and I have been playing with it despite the crackling, so I am trying to figure something else out.
But yeah, these KRKs are pretty solid quality, and I know I can get a solid tone out of them with some tweaking. I will definitely be trying the drive block and upping the presence on the guitar.