I upgraded to the Magni2Ü when it first came out and the difference between it and the original Magni was minimal but the sound is a little bit more authoritative and the bass has a bit more punch but without doubt the Modi is what elevates this computer system the most. I'm very tempted to upgrade my Modi to the new Modi Multibit but having a tough time pulling the trigger when this system already sounds so damn good.
Similar but opposite upgrade path, I had to upgrade from Magni to the Magni2Ü, because the original Magni was not keeping up with the sound delta from the Modi2Ü to Mimby. After the amplifier upgrade, very happy with the Mimby sound.