Well, to each his own... Personally, the drums rock my world on this one. Other sounds too, mostly, but organs are weak. Of course, there's no Mega Voice guitars and basses, a clear Yamaha advantage. But, great guitars on a compressed drum sound ain't no improvement, in my book!
Shame it's no walk in the park (which it ought to be) to connect the two together (S710 and GW-8L) and get the best of both worlds. Actually, thinking about it, those two ought to compliment each other quite well...
C'mon, arranger manufacturers! Get your sh*t together and pick a MIDI standard for connecting two arrangers..