Just received the Astrotec X34, Moxpad X2 and the Pistons and have the same problem with the pistons. Tried to swap around some of the tips from the other models and they seem to fit the earphone but still can't get a good seal. Also stole the tips off my JVC HA-FXD80-Z, again they fit but can't get a good seal. I Have large ear canals so I am always limited, most the tip varieties come in medium sizes. Ordered some double flange tips from Earphones Plus on amazon ( http://www.amazon.ca/dp/B00I13H3GC ) . Could not find any reviews on Head-Fi, I'll post my finding once I receive them, should be in the next few days. Also gonna try and review the great headphones I got thanks to this thread.
Thanks everyone! So far the reviews have been bang on!
Got the double flange tips today, they fit the Pistons perfectly and they seal very well. Build quality is decent, one tip is miscut causing it not to seal correctly, but I wont fault them for it at these prices. The tips have a lip on the inside shaft so they grab the nozzle and stay on tight. I would post pictures, but I don't have that permission yet. The pictures on amazon are accurate, they have a narrow depth ( about 7.5mm ) this seems to work well with the Pistons, the back of the second flange sits just in front of the housing . The sound after getting a good seal has improved dramatically as expected, the bass is now full and the mids have improved as well. Isolation hasn't improved from the stock tips, I can clearly hear the conversation of the tv show playing in the background of my room.
I also tried the tips with the Astrotec AX35's and the Moxpad X2's. They seat really well on the Astrotec's, much like the Piston's they lock into the groove on the nozzle. Not as happy about the seating on the Moxpad's. The Moxpad's don't have a cutout on the nozzle and the tip slides down too far, the end of the nozzle sits flush with the tip end. While using them with the AX35's I couldn't get them to seal, seems the narrow depth is to blame, I preferred the stock tips. As for the Moxpad's, they do seal well, but I can't see myself using them due to the seating.
Last impressions, they suit the pistons and my unusually large ear canals but they may not be for everyone. Possible applications are limited to the narrow depth, I would of liked deeper flanges. For the price definitely worth a try for people not wanting to spend a lot of money for tip rolling, especially in Canad where ordering over the border can sometimes be expensive.