In a medium glass bowl, mix together the melted butter, dark brown soft sugar, soy sauce, lemon juice and white wine. Stir until dark brown soft sugar has dissolved. Reserve a small amount to use as a basting sauce; the remainder is used as a marinade.
Place salmon fillets in a large resealable plastic bag. Pour in marinade, seal and turn to coat salmon. Refrigerate at least 1 hour, turning once.
Preheat outdoor barbecue for medium-high heat.
Lightly oil cooking grate. Place salmon on barbecue and discard marinade. Cook salmon for 3 to 4 minutes per side or until easily flaked with a fork. Baste with reserved sauce while barbecueing.