Oh no, he can definitely eat a sixline. Here's the thing, they are pure ambush predators, meaning they are not going to attack and devour, instead they set up shop and wait. The sixline is an evasive fish and may actually survive for a while, maybe a very long while or indefinitely. I had one big and fat and fast, and I thought he was going to be fine with my small painted at the time, and figure I had time to rehome the sixline. Well it went well for a while and I was very happy, then one day he was gone and Jabba had a big fat belly. You see, the painted are my favorites, they are smart and aggressive. While it's out of character, I've seen them chase down their prey. What they do is stalk and plan and eventually maneuver themselves into a route where they can catch a more elusive fish. They will even find out where they sleep and camp outside their their hidey hole to catch them when they come out in the morning. The only concern is size, while they can eat really large fish compared to their size, it can be dangerous. Many times when an angler eats a fish close to their own size, they die. I'm not sure if this phenomenon is just in captivity and if the conditions of their glass cage could have some blame. Perhaps in a larger tank, like you have, they have more room to roam, which stimulates their digestion. And because it's a coral tank, I'm sure your mg is reef level, mg has showed to be good for digestion.
I'm glad he's doing well, but I can't get the vid to load on my computer. I just wrote this up if you are interested, some good info if I do say so myself..
I've kept a few, my first going back 25 years. These are very difficult fish to keep and I am still very frustrated as to the success in keeping these guys long term. I do have some information I would like to share for those interested. Be forewarned, they are not for everyone and do take...
www.reef2reef.com