What Makes an Interface Stand Out from the Crowd

Are the internal electrical parts of a digital audio interface such as an
Mbox 2 or a MOTU Ultralite fairly similar. I am hearing that converters are
about the same. Like average home DA converters on CD/DVD players. Boards
are about the same. Even mic preamps are reasonably similar. That the key

Arny Krueger...

In some ways.

Arny Krueger...

Pick from a short list of AKM and Cirrus part numbers.

Arny Krueger...

Analog buffers tend to vary more.

USB, FW or PCI interface and DSP chips tend to vary more.

Arny Krueger...

I would expect to see considerably variation, there.

Arny Krueger...

That, too.

Invaluable: stable drivers.

differences are software, controls and connectors?