It still might be a non-Xerox ink compatibility issue of the sort that happens after awhile rather than instantly.
This page has a long discussion of how non-Xerox ink in a Phaser solid-ink-type printer can lead to printhead failures:http://www.fixyourownprinter.com/forums/inkjet/23195
and the official Xerox language about use of non-Xerox solid ink in their solid ink printers is, that they are not responsible for damage to printers owing to use of non-Xerox solid ink.
So it is accepted that as far as printhead failures are concerned, it's best to use standard Xerox solid ink. However, your question concerns a somewhat different issue: lots of ink going 'unused' or not passing through the usual heating process.
Possibly, just possibly, the problem you are having is, that ink is not being heated adequately by the printhead. I would like to ask whether there has been any degradation of printing performance by your printer lately?
This page discusses the issue of non-Xerox solid ink and increase in waste ink:http://reviews.costco.com/2070/11199319/xerox-xerox-phaser-8560n-color-solid-ink-printer-reviews/reviews.htm
specif. these paragraphs:
Solid ink is not for occasional printing - the cleaning cycles from under-use will cost a lot in ink and printer repair.
If you are printing 1000s of copies per month it appears to be a good choice.
This is something that you should have been warned about in Xerox's
guidelines for appropriate printer choice. The solid ink color
printers are designed for workgroups with a certain minimum threshold
of printing. I remember the literature giving the range of copies
per month. It's the technology, not the brand.
My recollection is that the solid ink is continually being heated,
and if it isn't used in printing, the system is prompted to do a
cleaning cycle to clear the ink feeding paths and waste ink recycles
into a bin. Printing a certain number of copies every day keeps
those paths clear, and so you don't have a cleaning cycle that dumps
way too much waste--and the waste ink does cost a lot. Also the
printers break down because they are not being used enough. Again
those repair charges are an onerous cost burden.
And another document states that a gasket leak in the cap/wipe/purge assembly gasket, could alter the amount of waste ink in the waste ink tray. So you might want to check for such a leaky gasket.