Topping A30 can drive them fine. They show up periodically on here. Magni 3 is a bit better for a bit more money. The A30 will be marginally warmer (probably not audibly so) than the magni 3, on account of the higher output impedance.
The thing with the DT990 is that it's a pretty bright headphone (beyer spike in full effect), and the 600Ohm version is not going to get all that much warmer even with high output impedance amps (say, 120Ohms). So just buy what looks nice and has enough voltage output.