Just to be clear for those who may not be familiar with Piezography... Epson OEM carts are wholly different from the refillable carts that Inkjetmall.com (and others) sell. SG, I'm not surprised you ended up using a ton of ink making those OEM carts work! Good on you (and Jose) for being creative, but that approach is definitely not recommended by Jon Cone.
A new set of (9) designed-to-be-refillable Carts for the 3880 is $155. It comes with one of the two chips necessary to make it work. The second small chip - typically pried off a used OEM cart - are the one's it doesn't come with and that Jeff is looking for.
Jeff, I'm in something of the same boat, as I'm contemplating the purchase of a second set of refillable carts so I can run a second Cone inkset. I'd love to hear of a source for those chips. Sure wish I had saved all those old 3800/3880 OEM carts I tossed in the trash over the years! I have a not-yet-opened set of Epson ink carts that I may end up cannibalizing, as I don't see myself returning to OEM K3. But, man, it hurts to think of tossing $500 worth of ink!
For clarification, I did not use jtoolman's method as he just worked it out recently, and the new resetter tool was not available back then either when I went to K7 in the second printer. I bought a new set of refillable carts and did it much as Cone suggested. Prime the new printer with OEM K3 ink to see if it works, then swap out and use the refillables with the K7 ink and the OEM chips that go under his chip (Which I got some from the college IT person's discards.).
However, it wasted a lot of K7 ink before my profiles began to smooth out and become usable. Nothing was anywhere near linear using the i1 Photo Pro 2 and QTR for a long time. I went through a lot of GO too (Residual black ink staining since it uses that cart position.) and had to buy a bigger bottle of it on the second order. I went through two purchases of K7 110ml bottles in just one month which seems absurd, but they like to sell ink too. The first set was just to get rid of some yellow and magenta staining, and some black tint for the clear GO ink too, left in the lines and printer head. Very white papers always had some residual color cast for quite some time even getting into the second batch. Do a MK/PK ink switch and some color staining may result too from the valve. These were new refillables, and not OEM flushed out ones, fwiw.
Of course you could also buy a second set of refillable carts and run their flush fluid through the printer to get rid of the K3 color set, but that runs up the bill as much as a second set of K7 used to flush the lines too. Plus, you still have to prime and flush out that fluid too with the K7 ink refills later.
As mentioned, on a new printer I would prime and run with the K7 if at all possible rather than use it as a big dollar flushing fluid later after the first run using the OEM color ink. Of course their method wants you to do otherwise in case of a bad printer which is probably a low percentage gamble if new and not a refurb, but they sell $$$ ink and flush fluid and extra carts for it too. There is a lot of ink in those lines and dampner assembly that I discovered when I tore into mine for a busted carriage repair. Personally, I'd run with the k7 and if the printer is bad, put in the OEM ink and let Epson handle it. They most likely will not tell you to return it with ink loaded anyway, and chances are low that it will be bad too. Beats shelling out $1000 for two K7 ink loads and all the paper waste to get it normalized and linear.
SG