Topping L50 Balanced Headphone Amp

Also in specs: Max output power: 350 mW (16 ohms), 540 mW (300 ohms) Output power: 3500mW x2@16Ω, 540mW x2@300Ω I assume the bottom one is correct -> very powerful while the top one is meh.

I'm not sure of your source on the claim, but Topping's website also shows these are TRS balanced inputs and TRS balanced passthrough. The information on the inputs/passthrough is highly likely to be correct. The jack is what I would expect to be compatible with Topping's TCT1, TCT2, TCT2, and TCRT1 series of cables. I did not learn of the existence of a 6.35mm TRS balanced jack until I saw the Topping D10 Balanced, so I am not the most knowledgeable. You can learn more about Topping's cables from their website if you're interested.