Yes, I know, I'm resurrecting an old thread...

I'm starting to find it frustrating that I don't have more control of
routing on the control panel of the Babyface.  My main computer has a
Multiface II, which lets me use hdspmixer to get all the same things
TotalMix would give you on Windows/MacOS, including routing that can do
anything, and I'm used to being able to setup any monitoring I want.
But that's a now-defunct breed of interface, which has a PCI-E host
card, a real Linux driver, and a nice GUI mixer application for Linux.

But because the Babyface is a class-compliant USB device that doesn't
have a real Linux driver or mixer app of its own, I can only do what the
control panel allows.  What I'd like to do is have a mono input on
channel 1 routed to the headphones on both sides (left/right), so it
isn't all in one ear, while a stereo signal coming in on channels 3&4 is
sent as stereo a pair to the headphones at the same time.  As far as I
can tell, it only handles inputs in stereo pairs, and I haven't found a
way to send a single channel to both sides.  I'm sure on Windows/MacOS,
the TotalMix application would let you do this.

This opens the larger question of where Linux recording is going now
that it seems interfaces with PCI-E host cards are becoming scarce, and
things seem to be moving toward all interfaces being USB.  Aside from
USB having latency issues we never suffered from PCI cards, what is this
going to mean when the Linux solution for every interface becomes, "Just
run in class-compliant mode," when that will not give you much control
over monitoring in situations like this.  Maybe I should have gotten a
digital mixer, since that would connect to the computer as a
class-compliant device, but mixing and monitoring would truly be handled
on-board.