This printer model has many more problems than just clogging of channels. If a full channel is gone (and that channel went slowly usually with missing nozzles from the middle of the nozzle check going outwards) this is often (mostly) a sign of a burned out channel. This and other forums that deal with the Epson x900 series printers are full of the same story.
Earlier in this thread I asked how many nozzles were firing in your MK (as we did not know yet that it was your VM channel) to determine if it was even advisable/possible to regain the nozzles that are not firing. Although I did not hear your response on that, I should have asked again. Sorry.
Generally on the x900x890 series printers, PiezoFlush will not be a magic cure-all that it is on x880 printers because the problems with the new printers are more inherent to the the head and cleaning assembly design as apposed to just clogged nozzles. That isn't to say that I haven't brought back nearly a dozen of the x890x900 series printers from the dead with PiezoFlush. But this resuscitation process was always performed on printers that were printing fine and then sat for nearly a year and only had dried ink/pigment to get rid of. If a print-head fails during frequent use, this is a sign of other parts failing. PiezoFlush is best used as a preventative (i.e.: putting a printer in PiezoFlush before a year long sit) or as a bring-back-from-dead after a printer has been let to dry. It will not fix mechanical issues that only appear to be clog related.
all the best,