I made some DIY new experiment yesterday, I swapped the original PK2 drivers from the DIY PK2 Docomo that I received 3 days ago, and placed original 150 ohm PK1 red film drivers instead. With stock foams on the shells, I can confirm that the PK1 drivers are clearly a true upgrade from PK2 drivers (without any surprise). Better imaging and instrument separation, overall clarity and details, more grainy mids, etc. But when it comes to bass area, I feel that the PK2 drivers are better (for those who wants more). PK1 bass is tight and clean, while the PK2 is more punchy and present, especially in mid-bass impact. Mids and highs are more smoothed out in PK2 drivers, but they performs really good too. I still believe that the original PK2 drivers included in the DIY from Chitty's store is already the best and good choice for Docomo shells, while PK1 drivers performs better in original PK shells. My advice is that It's better to keep that configuration then and do some fun mods into Docomo shells directly than trying to swap drivers. I really enjoy the form of the Docomo shells, as they sits very well and stays in place into my ears. A nice discover!