The RX6 has what I would call a slightly relaxed feel overall in comparison to the RX801. The uppers feel a bit more forgiving.
RX6 Flint Hills Edition Moonlight shoes
Shimano Flint Hills Edition RX6 “Moonlight” Shoes: Getting Rolling
I know now that wearing a RX6 and an RX8 at the same time, the RX8 one on one foot, the RX6 on the other, I couldn’t tell you which was which without looking.