I have fished the Deschutes quite a few time in my first life. Not only are there Steelhead in the river but some mighty fine redsides. My favorite Deschutes flies for either species have been, not in any partidular order:
Muddler Minnow #4-6
Cowdung #6
Brads Brat #6-8
Purple Joe #4-8

I Imagine you will be fishing from Maupin on down to the mouth? Lucky dog!