Focusrite Scarlett 2i2 worked out of the box with my Xubuntu 12.04. Even after many hours of continuous operation there are no instabilities, cyloning or distortions. Very reliable.

It works ok up to 96 kHz with JACK.

When switched on or being initialized by the computer there is a popping noise, so it's not recommended leaving the amp's volume knob on the max.

18i20 has 8 preamps and various digital I/O, Reported as working with Ubuntu 14.04, including MIDI. Mixer has to be configured from Windows for now.