I don't own a Dx6i so I don't know if this will work for you but on my OrangeRX T6xi, I am able to do mixing on the transmitter (where two channels are controlled by one stick). Using this, I am able to use a pair of TZ85As to drive The Honey Badger 2 (my featherweight) and will be doing so for its successor.

If you can't use transmitter mixing, then a secondary mixer also works well and has the same effect as described above but these can burn/break on you, leading to a loss of control.