Doubt about using direct box or not!

Last week I bought a M-Audio Profire, it is more or less same kind of interface. If I'm not mistake Profire is also 1 MOhm.

I tried it direct and through a DI Box, and couldn't notice the difference.
Perhaps if you are a bat or a dolphin you may notice some differences, but I guess you are not.

So my answer is that you don't need a DI Box.

Which DI box, though? There's definitely a difference in quality between the good and bad...