the s770 most of the same sounds as the Tyros 3, minus the S.Art2 and choir voices, but the drums are from T4 (so you probably won't notice much difference in a style designed for T4). The s970 actually uses the T4 chip, minus the choir voices (except Ooh and Aah) and minus all the S.Art 2 voices; megavoices are identical.
But since the s770 is missing some of the megavoices, you are probably hearing substitutions on the s770 that you enjoy more. (s770 has 23, s970 has 30, T4 has 43, mainly because of the extra choir sounds I mentioned)
But the s770 and the Genos most definitely do *not* have the same sound palette; go ahead and put a Genos style into the s770 to see what I mean. Especially any style that has vocals
DerekA is spot on; if you use a style for a lower keyboard, of course it will sound the same on the higher keyboard (it doesn't automatically pick 'better' sounds, like he said). But if you use the style from a higher keyboard, you'll definitely hear the difference on *some* when you play on a lower keyboard (not all, because some will pick the older voices anyway)
And yes that's in addition to DSP's; guitar distortion effects in particular, can *really* change the tonal characteristics of the instrument voice,
Hope that helps?
Mark
Mark