In a reddit AMA, when asked which guitar strings he uses, Steve Morse replies:
"I'm using Ernie Ball RPS Super Slinky. I think. They're the .09 set with the double wound ends. I recently switched from using .10's . That's for standard tuning. On detuned with Purple, we have 10's and 11's. The new metal type of EB strings sound great on detuned guitars, I think. Normally, for regular tuning, I'm using the standard sets."
The link to this particular post can be found here.