I use the Australian HF daily. I believe they recently went through an upgrade of the ground equipment but I couldn't tell you what it is. The comms quality in the aircraft doesn't seem to have changed much, but perhaps it is better for the ground operators. It is still a battle to use and sometimes you can spend 15 minutes trying to get through to someone. Partly this can be because they are busy with other aircraft that you can't hear.
They certainly do have multiple transmitter sites, though they had that prior to the recent upgrade. You can hear the effect of the multiple sites when you hear Brisbane talking to another aircraft and you can hardly hear the transmission, then they talk to you, switch to a more appropriate transmitter for your area, and they come through loud and clear. Or the opposite might happen, you hear them clearly talking to someone else then it goes all crappy when they talk to you, so you tell them "had you strength 4 when you were talking to QF123 but only strength 2 now", they'll change transmitters and come in strong again.