Not sure why QTR locks out Plain paper?
Could you set another media type and adjust the ink loading in QTR?
By QTR, do you mean Epson ABW, by any chance?
Have you tried the QTR list? A lot of folks with specific knowledge over there.
Does QTR, itself even support P8000?
Grayscale profile will only control gradation and not hue. Obviously, QTR or ABW can control hue.
Cheers,
Phil