Well, it can be a little complicated and it depends on the sound card driver as to what the recording sources are named. Here's how I did it:
1. open the windows mixer control and go to options/properties, check "playback" and check all the available volume controls, click OK.
2. look for the "Wave" playback source and un-mute or select this. Set the volume to about 50% as a starting point.
3. go to options/properties, check "recording", and check all the available recording sources, click ok.
4. select or un-mute the "All" or "Sum" or "Stereo Mix", or something similar. Set the volume to about 50% as a starting point. Make sure the other sources are de-selected or muted.
5. Leave the mixer open and start playing your web radio station in MJ. Open the sound recorder and select Options/Recording volume Auto/Start test. Now move the mixer slider for the "All", or "Sum" or whatever until the clipping distortion is somewhere between .1 and .5 percent. If you can't get it low enough, lower the playback volume from step 2. If you can't get it high enough, raise the playback volume from step 2.
6. Try a test recording and see how it sounds. Adjust the volume from step 4 up or down if needed.
7. Start the real recording.
This sounds like it would take forever, but it really only takes about 5 minutes.
Another option (that I haven't tried) would be to connect a cable from your sound card's line-out jack to the line-in jack. Then you could select "line-in" for the source in MJ and let it automatically adjust the optimum volume for you. If it couldn't get a good level automatically, you could adjust the "Wave" playback volume as in step 2 above.