The final block to produce the StockUpdate items will be this:

Observable.merge(
        settings.getMonitoredSymbols()
                .switchMap(symbols -> {
                    String query = createQuery(symbols);
                    String env =                                                              "store://datatables.org/alltableswithkeys";
                    return createFinancialStockUpdateObservable
                    (yahooService, query, env);
                }),
        settings.getMonitoredKeywords()
                .switchMap(keywords -> {
                            if (keywords.isEmpty()) {
                                return Observable.never();
                            }

                            String[] trackingKeywords = 
                            keywords.toArray(new String[0]);
                               final FilterQuery filterQuery 
                               = new FilterQuery()
                                    .track(trackingKeywords)
                                    .language("en");
return createTweetStockUpdateObservable
                            (configuration, trackingKeywords, 
                            filterQuery);
                        }
                )
)

Again, we can extract these blocks to simplify the flow and make it more explicit and readable.