I assume you are using a computer, If its windows, try windows media encoder. I use it on old XP computer and I can stream direct from internet to digital file as .wav. Other os systems may have similar direct encode to data, thus precluding the need for analog audio patch (noisy) cables. If you want to convert to MP3, try Prism available on CNET (Free). CNET has a wealth of such downloads. I use YouTube to play and pick off with Media Encoder,Great for finding one hit wonders. On caveat.... the streamed music will be somewhat audio compressed, so an audio DBX dynamic range expander placed in analog input path to amplifier will restore dynamic level ranges so audio does not sound so muffled.
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if computer is a tower or laptop; you csn get stereo mini jack to RCA cable to connect direct to stereo. One problem that will most likely arise is hum or ground loop noise. I purchased a BluTooth receiver from Amazon and I use streaming from smart phone. Very effective audio isolation.
Hope this edited version works for you