A bit past the 50 hour mark now. The bass is tightening/clearing up nicely so far. I did widen the ports in the back but, to my surprise, I did not notice a change when testing them(I about doubled the size of the port). I heard the same level. I did hear a change after leaving them alone for a day more of burn-in though. As crossed my mind before it now sounds very close to the PK2. It no longer sounds like a PK2 with big, somewhat congested bass. I would say the PK2 mid-bass hump gives it a slight bit more weight there and in the vocals now. So, the Maximo is ever so slightly more flat. I like the tone of the Maximo treble slightly more. The detail level is the same also.
Depending on how far in you insert them you also have near the soundstage of the PK2. Slightly less than the Yuin until you insert deeper and increase the isolation where the soundstage starts to compress. Of course moving the drivers closer and forcing the drivers to work harder to move air(needing more volume) does give them more detail. It is cool to have the option since there is really no stem. More isolation just on depth without needing to change tips. Even deeply inserted, footstep noise is noticably less than with other IEMs. Of course there is more comfort if they aren't in as far.
I like their balance and how they are an easy listen. No harshness, fatigue, or glaring flaw in this phone. Everything is done well across the spectrum. Good bass, good mids, good treble, good extension, etc. As such it is a safe bet that many people will like them. At the price everyone should. The X3's are about twice the price and the Yuin's are two and a half times the price. Neither has better included accessories. Mine might improve even more with more burn-in and these are the old version. Maximo has improved with the second version and are supporting the product with a lifetime warranty and listening to our feedback. Kudos! It is a very nice product!