SDR=Software-Defined Radio. In my view, having never actually used one, the biggest value of an SDR is that you can record multiple frequencies at the same time.
Why is that important? Because "openings" (brief windows of time) for DX from a specific location usually occur at the same time. Whether it is, on the AM Broadcast Band, Australia in the middle of the night, or Nampa, Idaho, from Vancouver at high noon in the winter.
As to the earlier comments that Ears are more important than improvements in Equipment, I would strongly disagree. In a large Urban area, speaking from personal experience, the CCRadio-EP with TERK tuned AM Loop and an audio amplifier is better than the Lafayette HA-230 with 4' tuned box loop I had in the late 1960s. At less than one twelfth the price, if you take inflation into account.
As well as the multi-frequency monitoring of SDRs, and the capability of simultaneous recording all those audio streams on a computer, there is now the ability to eliminate a local station and hear what is underneath (on the same frequency) by a type of phasing. A Vancouver DX'er (Bill Wilson is the name that comes to mind, but I could be wrong) in the late 1960s was in Physics at UBC, came up with the idea, but now there is equipment you can buy to do it. I know of two reception reports in the last few years at CHQT-880 in Edmonton from listeners quite close to the Seattle and New York City stations on 880. The typical setup is two loop antennas pointed in different directions, where you subtract the audio of the one getting only the local station from the other that is doing its best to null out your local station.
I am sure there are other techniques. Graphic equalizers could make it easier to make out a hard to hear ID on a recording by trying different settings. Noise elimination software can also get rid of consistent background noise, which would also make things easier to hear.