The 4KZ 1620 kHz 400-watt relay is quite easy to hear at my location, despite the 12,800 km distance.
Not so with their 1.3 kW station on 5055 kHz! After a few futile (albeit random) attempts, I decided in February to monitor and record three top of the hours every day. I also wanted to do an A-B comparison between the Airspy HF+ and the SDRPlay RSP1A. So both were connected to the same antenna, two different PCs with HDSDR running on both. After quite a number of days, the signal was finally readable.
The HF+ is known to be a very sensitive SDR, while the RSP1A is more average when microvolts are measured. So, there "should" be a difference in audio recovery, at least on threshold signals. There was. When signals are very weak and the noise floor is low, better sensitivity is indeed audible. Here is how 4KZ was heard at the time. Headphones recommended.
The 4KZ General Manger Al Kirton is a DX-friendy guy, and sent off a proper QSL card with a sticker and info in the mail.