The DGX line used to be rather simplified prior to DGX-670; just two sections of an accompaniment, both placed on a single button, like on PSR-E series, no voice editing or mixer... As if Yamaha didn't want to scare away customers who were afraid of buttons. But looks like the XG-lite voices were playable on the previous models. Now DGX is much closer to PSR, and Yamaha decided that XG is "too much information"... To tell the truth I didn't notice that on SX900 there was no XG folder either. When I had an advanced entry-level PSR-550 (Sqk, I think you had one as well and switched to Casio WK-3800 or something) I remember that each voice was important to me; now it seems that I play only the basic and the tastiest ones, and don't pay much attention to "smaller" ones... But I know for sure that if a new PSR didn't have an old "Slow Strings" sound, that would be a problem for me. Yamaha adds new strings all the time, they are fun at first, but I can't really use them with piano; so I can see that some of those XG sounds are just as important to you.