No. In my opinion, there is no reason to buy a Jotunheim if you won't use balanced. If you already have the Magni 2, you'd be far better of getting the Modi 2 MB than a Jot, and it would be cheaper.
Oh, and hello everyone, I guess this is my first post here. Funny, I actually just finished building a balanced cable for my HD650s. I was actually about to come here confused because the balanced cable was just a little bit quieter than the stock SE cable was until I realized that I had it on low gain and that the balanced out on low gain as almost as loud as the SE out on high. I'm much happier with the output for the HD650s now. With SE I found myself turning the knob a bit more than I'd like for quieter stuff like classical. I'm really impressed with this thing now.
Quick backstory, I've actually had the HD650s for about a month and the Jotunheim came in a week ago. This is my first setup of this quality and I just can't pry myself away from listening to everything I own all over again now. I'd say I can't tell you how happy I am to finally have a decent listening setup, but I'm sure you've all experienced the same. Now let's see how long I can stay satisfied with this