I hear ya. Steelhead are a bigger fish and need a good rod with backbone. I think you would really be pushing the limits at both ends. Crappie are generally 1-2 pounds, Steelhead can get up to 50 pounds, averaging about 8 pounds. The trouble your going to run into is matching line weight and lure weight to the reel/rod combo. You will be hard pressed to use high strength superlines for Crappie and you will be hard pressed to bring a 50 pound Steelhead on 4 pound mono. That assumes you can find a reel that can be spooled with both lines.
The other issue you face is rippin lips. A strong backbone rod won't flex enough and you may rip the hook out of the mouth every time you set the hook.
You would be better off using two rods, one geared for Crappie and the other geared for Steelhead. Have you checked out the St. Croix Salmon/Steelhead series line of rods?
HOI Crappie Club
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Quick, someone teach me how to fish so I can win this tournament!!!