Others have also frequently commented on the TX-9800 as one of the best stock tuners for DX reception, so this is not surprising to me. When you start splitting hairs for DX reception, the IF filter bandwidth makes a huge difference, the more narrow, usually the better the reception. The stock 600T filters are fairly wide, even in the most narrow setting. They just added more 280 kHz filters in series to make the "narrow" filter. These are the old 4 pin double filters, but easily replaced with 2 typical 3 pin types (per each 4 pin) and sockets. You connect the 3rd pin of filter one to 1st pin of filter two on the socket, and cut the socket leads for those 2 (there are no holes on the tuner circuit board for those middle pins).