WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
Building, troubleshooting and testing of these amplifiers should only be
performed by someone who is thoroughly familiar with
the safety precautions around high voltages.
From my experience the Aikidos work well as a headphone amp for high impedance 'phones and SOME low impedance 'phones. It's not entirely a question of impedance value. E.G. AKG 701s don't work that well with Aikidos I've heard, but might with a version based on the ECC99 tubes in the picture.
The two boards at the bottom of the first picture are mono line stage/headphone capable amps. one or the other, depends how it's configured. These would make a great line stage or HP amp (see proviso above) and the Janus regulator would be good for powering them. I think this is the Janus with the built in rectifier, filters and filament reg.
Yes, most definitely will the Aikido and Janus make a good sounding line stage. Tube dependant of course. It might even surpass your "great" preamp. I lean towards the Aikidos with 6DJ8 for a clean, fast sound. 6CG7s (a nine pin version of the 6SN7) will sound more tubey, in my experience.