Have You tried Image Armor. Image Armor Pretreatment for DTG inks I run two GT-782's and just tried it. I was amazed. It also works well on 50/50 blends.
Where are you located? In the USA, Brother sells a smaller size (4 kg bottle instead of the 16 kg pail) for less than $170.00 last time I saw it. Not sure if this same size is sold worldwide.We just can't afford a $600.00 pretreat solution anymore.