[CentOS] USB audio on Centos-7

I'm using Centos-7 on my PC, with ASUS  motherboard. internal audio
has always worked fine EXCEPT that I can never get audio input (for
recording) to work. I want to feed audio from a phono turntable and
from a cassette deck. I use a phono preamp for the turntable, or 
directly connect the tape deck.

but either nothing, or low level with  horrible distortion.

so, I gave up (after years of intermittent battles) and bought a
Behringer UFO202, which looks like it should work fine with Linux.
It allegedly  uses a TI PCM2902 chipset, which many online postings
claim works fine with various flavors of Linux. This device has
a USB port, a pair of line in and line out jacks, a phono jack, a
headphone volume control, and a switch to change the line in to
phono in.

I can use headphones plugged into the UFO202 to listen to audio
playing on the computer, but I cannot for the life of me figure out
how to feed audio into the UFO202 (via its line in RCA jacks) and 
have it come out speakers or phones connected to the computer.

I've poked and proded at alsamixer, the mate sound tool, and pavucontrol.
No useful results.

Pavucontrol, in its input section, does show the device listed, and
it shows activity on its level mater when there is audio input via
the line in jacks on the UFO202. Disconnect the line input and the
activity ceases.

(Mate sound control also lists the device, but I don't even get an
indication of any input at all, as I described above for pavucontrol.)

but I simply cannot figure out how to get that audio to play in any
audible way.

I know that USB audio input works, because I have a Plantronics USB
headset with microphone that I use often to converse online, and it
works nicely.

(and a possibly separate issue: how the heck does one point Audacity
to a USB input? Can't find anything in its UI, and there's darn little
help online that is actually helpful, in this regard.)

Can you sense my frustration here?

I'd appreciate any help that is actually helpful,... perhaps someone
who reads this actually has one of these things and has made it work?

thanks in advance!

Fred
-- 
---- Fred Smith -- fredex at fcshome.stoneham.ma.us -----------------------------
                         God made him who had no sin
                      to be sin for us, so that in him
                 we might become the righteousness of God."
--------------------------- Corinthians 5:21 ---------------------------------