Tye, there are so many factors to be considered. You have an Audya now, and consider what would be gained by adding an SD7. I don't think much. The SD9: more, certainly, if you think the Launch Pad, later sampling, more RAM, guitars, and so on would tip the scales for you. I think the Launch pad is a huge, little understood feature for some players that like to create. The SD40 and SD90 are great choices for do everything modules, and the Pa4X is a great keyboard that has it all for me as a performance keyboard.

Good luck and consider I often get gear lust when I already have more than enough already. I just like the challenge of something new.