I'm curious as to whether the matte-->photo black switching process wastes color ink as well as black (and if there is any rational explanation for this behavior, profit motive aside).
Gian
It certainly does waste all your inks, and always has on the R2400/2880. And every time you change any of the other cartridges. I have my dump lines run out to a catch bottle rather than the internal waste pad, and you would be amazed how much ink I regularly tip down the sink from that little bottle. It is tempting to think that this is how Epson make their bottom line, but there may be sound technical reasons for doing it this way.
According to Epson, cartridge change on the R2400 uses 0.386 gram per cart, whereas a standard cleaning cycle uses 0.194 gram per cart. It's probably similar on the R2880, except that you have even smaller cartridges (which was a really inexplicable move on Epson's part, unless you take the view that they simply want to maximise profits, because the smaller the cart, the more often you have to change them, and the more ink you waste).
So, to mitigate all this - you will waste the same amount of ink whether you change one, two, or however many cartridges
at one time. OK? So try to time your matt/gloss cartridge swap to a point when at least one other cart needs changing too. Then stick with matt or gloss until another cart change is required. This obviously entails batching up your matt/gloss work into discrete print runs. Also, if a cartridge runs out and needs changing, swap out any others which are really low at the same point, and just do one line purge cycle.
Even then, these little printers drink the ink. Even at my hobbyist level, I use around 3-4 cartridges a month, so 30-40 GBP at the cheapest I can find them here in the UK. That's why the pros round here are very sensibly using the R3880 and larger. But the 2400/2880 are lovely printers.
John