I have both kept together. Goonch's are not very active just sit most of the time and Wallago's swim around the tank. So if you want activity get a Wallago. If you don't care just want to keep a Monster catfish then get a Goonch.
My Attu eats whatever is easy to catch and can fit in there mouth. Maybe its become lazy since it doesn't have to really hunt for food. He eats pellets as they float by him. He'll eat frozen fish live feeders that don't swim away. I do nothing special to the water. I keep him with other fish that are to big to eat. Just a clean tank like you would for any fish.
Thanks! How much did yours cost you? And what temp do you keep the water. Like I know the Goonch prefers high current and lower temps. And the Goonch grows very slowly does the Attu as well?