Thanks for the answer.
Based on my experience, initial fill is only reasonable if piezo flush solution is used for every cartridge. Otherwise, ink consumption can be awfull. I have tried to save some bucks by limiting spare cartridges to clogged channels: it costed me more!!
The most severe clogged color was PK/MK (nearly no output). After 3 initial fill (with piezo flush solution on corresponding channels), 90% was recovered at the third flush but still printing in black (I suppose that the piezo flush solution has liberated the damper at this stage). At the fourth initial fill, piezo solution was printed with a completely unclogged channel. I loose about 500 to 600 ml of good ink in the process!
By the way, if the ink consumption, based on the net available infos, is 115 ml for an initial refill process and 53 ml for a CL3 cleaning cycle, it seems to me that not so much CL3 cycles would be necessary to replace ink in the lines, as suggested by Jon. But may be his assessment is based on experience, mine is not! I used during the life of my 4900, a lot of cleaning cycles (CL1, CL2, CL3) with a head apparently still unfried. The rule that I applied since the beginning was: no more than 2 to 3 cleaning cycles in 24 hours. May be that was the key to preserve from the full loose of the head?
In other words, I try to figure out if there could be a reasonable unclog procedure, with respect to true ink consumption. First experience with piezo flush solution, even if successfull for unclogging the head (great!), is unviable from an economical point of view. This leads me progressivly but surely to the conclusion that a move to Canon IPF with PF05 heads could be the best fix!
This does in no way limit the merit of Inkjet Mall for developing a rescue procedure for Epson printers users (at least someone is providing some help!). But all this highlights, from my point of view, unacceptable commercial practice from Epson, who continues to sell X900 series without shame. Ethically at least, it pushes to a more radical solution...