The simplest method is to play the juno as a live instrument, skipping the editor etc (that can come later). Choose your sound from the front panel of juno. SONAR can record the playing, and playing back using MIDI. Depending on the hardware synth, it will use old style midi cables into a midi interface (many audio interfaces also have midi input/output built-in) or USB. Record and play back into the Juno to make sure that works as advertised.
Then you take the hardware audio outputs of the Juno and connect them to the audio line inputs (or mic/line combo inputs) of your music interface. You can then record your midi performance on the Juno as audio, just like singing or guitar. Bob above gives a more complete account. If you give your specs - like your audio interface, we can help more.
You can, of course, edit the midi info before recording audio (or after, tho you will have to re-record the audio then). And you can "edit" the audio, adding effects and volume envelopes or chopping the audio into smaller bits and re-arranging them.
Once you've got that part done, you can learn to choose patches from SONAR, edit your Juno from the computer if you wish to bypass JUno's edit panel.
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