Internal hubs are great, but they do tend to add weight to the bike. A big reason derailleur systems are used on folders is to shave some weight off. There are lots of hub options out there. You should determine your budget as that will quickly narrow the field (or keep it open to the high end too). Also determine what sort of gear range you want, as that might also greatly limit the field. Why did you purchase the P9 instead of the P7i (or other internal model)?