bongomania
Commercial User
I don't see why you need a DI at all. As I see it, all a basic DI does is convert a high impedance source into one suitable for a mic level XLR input.
You answered it yourself. Impedance is completely different from amplitude. Now, if the mixer you're plugging into happens to have line inputs with a z in (input impedance) that's ideal for the z out of your bass, then great- that's lucky and it will work fine. But not all mixers have suitable z in at the 1/4" inputs, especially for passive basses. It will still "work", but the signal will be struggling harder to transfer from the bass to the mixer, and your tone may suffer.