I play keyboards in a band.
I have Roland ep7 (electric piano)
Roland Alpha Juno II
Yamaha DX7 II
Now I want to get lot of new GOOD sounds.
Which one is better? JV 1080, JV 2080 or SC-880?
Which one of my keyboards is best using the sound module?
Where and how can I download sounds for dx7?

It depends on what you want to do with the module. Is a big collection of great sounds all you want, you should take the SC880, but it is only a very big soundcanvas. That means (almost)no editing! If you want to design sounds, or use filter sweeps etc. i'd take (and have taken) the JV1080. Furthermore, you can expand it to your needs whenever you want!

test