If the signal block diagram attached is of good enough resolution study that.
If not, put "Xenyx block diagram" into Google and get the .pdf (Behringer stupidly no longer include such data in their handbooks and the .pdf is too big for HR to handle!).
Now I know some people wail and say "Ooo! I can't handle technical diagrams!" Well I say "tough" because you HAF T!
If you drive you must be able to read a map (GPS is not infallible!). If you don't drive the Underground diagram? My point is, diagrams are the way we make sense of the world (that Berry diagram is no more an "accurate" representation of the actual circuitry than is the UG map!). You can follow a signal thru' from mic input to output.
Yes, the mixer can feed a hi fi amp. The good thing about audio is that you can plug almost anything into anything else and it won't smoke. May not work or might hum like stink so keep gains and volumes low and advance slowly.
Yes you can record a stereo mix via usb but the system is limited to 16bits and often the usb send back to these mixers is rather noisy. Latency (Googe again!) is also likley to be poor. I ran
a Xenyx 802 into an M-A 2496 (24 bits) soundcard for several years and Son got very good results. You could do the same*. The mixer has since been replaced with an Allen and Heath ZED10, rather better!
*If you have a laptop or if fitting an internal card is scary, look for a modest Audio Interface such as the M-
A Fast track pro,
Tascam US 144MK2. These can often be found in CashConverter shop and their ilk.
Dave.