HELP out a new guy with some speakers! Please READ

[TheOverallKyle]

Hey all that are into music!
I'm sorta new to this "Studio" thing. I have a stereo system made by JBL thats REALLY old. Instead of having to spend hundreds of dollars on decent monitors, i was gonna stay with what I had. The speakers are bare wire and passive, they are connected to a giant amp

Here are the specs:
JBL J2045 speakers
Kenwood KRX-89 amplifier and tuner
Behringer UCA202 interface (could upgrade if necessary)


The JBL speakers are connected to the amplifier, and the amplifier has 2 sets of RCA inputs on the back. One pair says 'CD' and the other says 'Video/Aux'. Could I connect the USB interface that I have to the system via RCA to play the audio through the speakers?
Another theory that I could come up with was buying a cassette tape that you can connect and audio source like an MP3 player by inserting the 1/8" ending from the tape into the headphones spot in the MP3 player. Could this too be a way to listen to the audio while mixing?

If there is any other information that could help determine the solution, just ask

 

[altitude909]

either of those inputs will be ok

 

[TheOverallKyle]

Thanks! will try one of the two options! Sorry guys for double post

 

[TheChikenMaster]

You can use those connections, try it already!!

 

[dementedchord]

some of the better recievers even have a direct in for the amp... if so use IT... will look like a little u shape of metal... jumpered between the amp in and the preamp out...