Of course, a yamaha keyboard with a lot of buttons like your s990 is very good too.
The 2 systems have their own interest.
I personnaly use my Ketron SD1 on some gigs, and love to take my vArranger + SD2, on some other gigs. Depend on the context...
Dan
Dan good luck with the Varranger....but you would never do my type of gigs using something like that for so many navagational and sound reasons..... but if it works for you and your happy ENJOY IT!!!