RME ADI-2 Pro at $1600 or ADI-2 DAC at $900 is one of the best choices one can make in pro audio or audiophile worlds under $3000. But these are meant for desktop use - although, technically, you can stack and power it with a USB powerbank inside the backpack. RME Babyface Pro FS is an equally great option at $700, if you want something more portable - it comes with no battery, draws power from laptop or phone however; and sports XLR/TRS inputs for recording audio too, if you wish; and certainly not for dropping into jeans pocket while walking. It's time RME stepped outside pro world and did a truly portable and battery-powered DAC/Amp based on ADI-2 or Babyface circuits. And maybe add Bluetooth and SD card slot to the same. Sound Devices MixPre-3/6 -II and Sony PCM D-100, if you still want to exploit pro audio interfaces+recorders+players for portable audiophile use with added burden of batteries. All these come with super neutral sound signatures, super pristine quality preamps for external microphones and very powerful amps for headphones/IEMs. Nay, wanna remain in audiophile world using only truly portable audiophile products on the go? Dozens of options as you can see around here. Cayin N3 Pro at $500 is a very good option as estimated with specs and by the proven success of N8, it's bigger brother with similar specs, to replace your Mojo stack. Both tube/solid state 3.5mm and solid state 4.4mm offer great amount of power for such a small device and completely sufficient for most IEMs including your U12t and full-size dynamic headphones. If you still want more power, there a few new DAC/Amps or DAPs with 1W or more outputs at 3.5mm.