Hi Ralf,
that sounds bad. I have a Scarlett 18i8 first-gen and never had such
problems. Did you do any other testing in addition to subjective
listening tests? Maybe hook up an oscilloscope to the outputs?
There is a problem with my Scarlett where sometimes I get horrible
crackling noise. Restarting JACK fixes this. Could this be your issue
as well?
Btw. the only available control by alsamixer is
"Clock Source".
This means that the ALSA mixer kernel code doesn't recognize the device
yet and doesn't load the "scarlett mixer quirk". There should be a huge
number of controls. Without being able to control the mixer matrix, the
Scarlett is much less useful... It should be relatively easy to insert
the product ID of the 2nd-gen into the alsa code, though. Have you
patched & compiled a kernel before?
Best,
Johannes