A new urban legend is born: The TT₂ is «too weak» for the HEDDphone! This despite power reserves outperforming most dedicated headphone amps: 18 W at 8 Ω, 1.15 W at 300 Ω; that will be about 5 W at 42 Ω in balanced mode or 2,5 W single-ended. Add to this that the TT₂'s output stage is possibly the most advanced amplifier design («DX, digital class A») on the planet, a «test run» for Chord Electronic's future amplifier concept announced to offer ultimate neutrality and transparency, the litteral wire with gain.
I haven't heard the TT₂, but am a big fan of Chord DACs with their direct-to-DAC headphone outputs. The HEDDphone sounds wonderful on my DAVE, which has far less power reserves. And it still sounds wonderful driven by my Hugo₂.
So it's clear to me that you're about to create a similar myth about how hard to drive it is as has been popular quite a while for the HD 800 – actually an easy load, but a headphone with a characteristic coloration that people have tried to fight with coloring amplifiers (looking for tonal synergies in the sense of compensating flaws). And yes, the HEDDphone also has a
characteristic coloration that needs to be taken care of, but using amplifier colorations (= harmonic distortion) for this task is an erroneous path. I for one use a parametric equalizer and get great results with a source/amp that I consider as neutral as it gets – in the interest of ultimate transparency with minimal harmonic distortion. No need for astronomic power reserves in exchange for effective sound quality.