I never heard of the Lynx 22, but I have heard of AudioFire. In fact, I considered the AudioFire 2 before settling for the Apogee Duet; but had to make my choice without being able to audition either. I went with the Apogee purely on word-of-mouth. No regrets, but that says zero about SQ differences between the two.
My reply had more to do with sound cards in general - not a fan. So I tend to default to: "Why not avoid sound cards entirely and go with a USB DAC?". After your response, I looked for myself; and see that it isn't a sure thing that a USB DAC is going to work with Linux - especially if async USB is part of the deal. Sorry for not checking personally first.
Is there a reason why you have rejected the highly regarded ASUS Xonar STX?
It looks like they can work with Linux. Being somewhat timid, it would be my first choice in terms of SQ on Linux. If nothing else, you won't be starved for feedback on the Xonars.
Back to the two products that you mention. The ffado project seems like the better bet for long term driver support. However, the 1/4" balanced analog outs may be limiting in terms of amp options; or were you going to use the AudioFire 2's headphone out? That is what I opted to do with Apogee Duet, and it is fine with the easy to drive Grados.
A couple points with the L22:
- What are the cost of the XLR-to-RCA adapters if they are not included? (And, yes. The manual does give you the info you would need to roll your own.)
- Unless they have slip-streamed updated components, the components must date back at least 8 years (this thing originally shipped with Windows 98 and Mac OS 9 drivers!). Perhaps my concern is overblown if subsequent generations of DACs offer little in the way of SQ improvements.
Both devices are stuck on interfaces that are on the way out. Not a huge concern, as it will be years before either is likely to present a hardship; but I'm sure you already know that.