Here's what you do. First off, "YES" you can have "two tones" per patch. The way the sounds are made up on the Juno-D are as follows:
You have the "Preset Patches", these are the voices you'll select for normal play. For example the sounds that will appear under each of the category buttons.
Then you have "Tones". The "Tones" on the Juno-D are the "smallest element of sound". The tones "combined" in multiples of (two) are what make up the patches. For example, a "piano and string" combination. To make this "patch" you'll select the individual tones to create it. You'll select a piano tone, and a string tone. Piano will be "Upper", and Strings will be "Lower".
To access the "individual tones" you can do this in two ways. I STRONGLY SUGGEST USING THE EDITOR SOFTWARE!!!!! The software is very easy to use, and you get access to so many paramters on one screen.
To see all the tones, select a "patch" then press the PARAM button under the "EDIT" section. This button is located next to the button that says "effects". Once you press that button the first tone you'll see will be the "upper". If you want to add a second tone, while in the PARAM mode press the "Lower" button until the lower buttons light is the only one lit. This will allow you to select the second tone. To hear them both together, go to the far right of the keyboard and locate the "key mode" button (it's over by the patch modify section). Press this button until "dual" is lit. You'll then be able to hear both tones.
The manual actually IMO does a good job at explaining how to do this... If you still have the software download it to your computer and get a USB cable. That software will be your "BEST FRIEND" when editing voices. You can do EVERYTHING from the software.
Good luck.
Squeak
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GEAR: Yamaha MOXF-6, Casio MZX-500, Roland Juno-Di, M-Audio Venom, Roland RS-70, Yamaha PSR S700, M-Audio Axiom Pro-61 (Midi Controller). SOFTWARE: Mixcraft-7, PowerTracks Pro Audio 2013, Beat Thang Virtual, Dimension Le.