Hi James!
A Bryston Headphone Interface should be at least as good as this one (999 €):

Input impedance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .50 kΩ
Maximum amplification. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 dB
Frequency response. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Hz - 100 kHz (-1 dB)
T.H.D.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.001% at 170 mW / 250 Ω
Channel separation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . > 89 dB
Output power. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100 mW / 600 Ω
170 mW / 250 Ω
150 mW / 30 Ω
Unweighted signal-to-noise ratio. . . . . . . . . . . . . . . . . . . . . . . . . . . . . > 100 dB
Output impedances. . . . . . . . . . . . . . . . . . . . . . . . . .Line Out (depending on the connected device),
100 Ω headphone output
Power consumption. . . . . . . . . . . . . . . . . . . . . . . . . .< 15 W via internal, controlled power pack
Audio connections. . . . . . . . . . . . . . . . . . . . . . . . . . Headphone socket, 1 Line output,
2 Audio inputs (gold-plated RCA sockets)
Hand built with discrete electronic components.
I've heard this device several times together with a Beyerdynamic T1 and it was simply phenomenal! It's like if there's only music - all technology steps back and let you enjoy the pure sound. Really amazing.