The topping a90 hpa has more power then the rme adi-2 pro headphone in balanced mode, so it should be able to drive the iFi IESL electrostatic energizer.
Rme adi-2 pro:
Balanced Phones mode
As before, but:
• Output levels at 0 dBFS: Hi-Power off +13 dBu (3.46 V), Hi-Power On +28 dBu (19.5 V)