// sync only for dojo/store/Memory
var store = filteringSelect1.store;
filteringSelect1.set("value", store.getIdentity(store.data[0]));

when(store.query(function(item, index, items) {
    return index == 0;
}), function(results) {
    filteringSelect2.set("value", store.getIdentity(results[0]));
});

restStore.query({ index: 0 }).then(function(item) {
    filteringSelect1.set("value", restStore.getIdentity(item));
});