The USB is to connect to a PC so software like Audacity can be used to copy the record in real time. If it's a cheap POS turntable, then yes, it may well have bluetooth out, so you may be able to bluetooth it to your AVR. It will sound horrendous, but many customers will be over the moon just to play their old records. Of course, plugging the RCA out into the AVR via the 3400's built in-phono stage is ideal...
This industry is not getting cheaper and cheaper, we're simply convincing ourselves that we have to push the cheapest option to customers. #makesonosgreatagain
