"He who marches out of step hears another drum." ~ Ken Kesey
If the 50/50 discharges reasonably well (most black 50/50s don't) then I would do DC UB + HSA White. Wash test this first, not all HSA ink will adhere over a discharge base, many will look great out the dryer and flake and crack off after washing. If they don't discharge well you can revolve a screen of HSA but I would consider using 2 screens with a dye blocking HSA for the UB. This is shirt, dye and ink dependent, some HSAs have surprising bleed resistance, others don't. CCI Pure White is an HSA, fyi. Decent product at a good price but there's no other inks in that system from CCI so you'll need to test compatibility with other HSA systems. It is NOT compatible with standard water based inks may or may not be ok over a DC UB. Hope that helps a little.