In a Dutch oven, cook fettuccine according to package directions, adding the asparagus during the last 2 minutes of cooking; drain.
In a large skillet, combine the water, broth, 1 cup champagne, onion, tarragon and 1/4 teaspoon pepper. Bring to a boil. Reduce heat; add fillets and poach, uncovered, for 8-10 minutes or until fish flakes easily with a fork.
In a small saucepan, bring the remaining champagne, garlic, basil, brown sugar, salt and remaining pepper to a boil; cook until reduced to 1/2 cup. Whisk in butter until melted. Pour over fettuccine mixture; toss to coat. Serve with salmon.