Yes, the sx700 and the s970/s975 share the same sound library, except that the s975 has 4 additional packs of expansions pre-installed (which are *mostly* also pre-installed on the sx700 as well)
THe e473 not only doesn't share the same sounds, the interface is *completely* different, and it certainly won't load your s970 registrations. The sx700 will; HOWEVER anything that used s970/s975 Audio styles won't be present, nor is there any way to put audio styles in the sx700. And it's no longer possible to even download the s970 audio styles in the first place, ever since they re-did the musicsoft website.
So if any of your files depending on the audio styles, or the built in pre-installed expansion packs, you could run into issues, but otherwise everything else is there.
Mark