I’m aware of the jumper mod. It only filters signal coming in from DACs. The issue with driving 600 Ohm cans is only in part due to power. As Wave Theory touches on above, it’s all also the design of the amplification circuit and the quality of the parts used - this impacts on whether they can deliver the power quick enough/control the drivers.
Singxer’s SA-1 sounds brilliant, but it can’t do really hard to drive cans.