He sent me a pair of K3 PRO to try out, and so far they've seemed to be a step up! As I write some promissing commments, I can say that they've been burned in at around 60 hours.
Dark Gray tuning nozzles:
These are tuned to down-size the higher scale midrange peak (around 5 - 8,000hz) from sounding overly bright. So, you don't get much of that sometimes harsh or sibilant results that comes with the original K3 on certain genre's or songs chosen for your listening experience. In return, you get better image, resolution, and slightly bigger soundstage. Bravo!
Silver tuning nozzles:
These are tuned to be even more warmer (lowering the midrange even more at around 3 - 7,500hz), while miraculously maintaining even better hi-end treble with details and refinement. Resolution is also better than the original K3's, as well.
About the bass:
On both the Dark Gray or Silver tuned nozzles the bass sounds quite like each other, no matter which tuned nozzle you prefer to use. Which, I personally say, is a good thing! Since the new graphene drivers really sounds impressive!
So, If you just like a bright sounding signature, just get the K3's, BUT if you like your earphones a little WARMER than bright, go for the K3 PRO.