Shouldn't be a prob, the 6cell flat pac when freshly charger should have almost as much voltage as a fully charged 2S lipo. I don't thonk the extra 0.1 or 0.2v is going to matter.

What does the 1600 Orion indicate fresh off charger? Most of mine get close to 1.34-1.36v/cell. The 2S will be 8.4-8.42v so they should be close. Your rx has already been seeing the high volts from the flat pac.