Here are the Tech Specs on one of the new DSD512 albums at NativeDSD:
"We are pleased to announce the availability of Groove Note releases in DSD 128, DSD 256, and DSD 512 in addition to the original DSD 64 releases. These higher bit rate DSD 128, DSD 256, and DSD 512 releases are all pure DSD created. They are not up samplings, for there are no PCM or DXD conversions involved in their production. They are re-modulations of the original DSD 64 encoding modulation that produced the DSD 64 releases. The sonic advantage to these new Stereo DSD 128, DSD 256, and DSD 512 releases, as with all higher DSD bit rate releases, is the wider frequency passband prior to the onset of modulation noise. This results in the listener’s DAC using gentler and more phase linear filters for playback of the music."
I had a fairly extensive conversation with David Elias. David is a pioneer in both DSD recording and also a big supporter of MQA for streaming and portable use. He emphasized that these DSD512 albums are not simple up samples but true re-modulations 100% in the DSD domain. I admit to not totally understanding the entire process but I can say that they are amazing sounding and very nice improvements.
I have David's 5 original DSD recorded albums and 4 that have been reworked to DSD512. I believe they are fairly nice improvements. I also have 2 Vanessa Fernandez albums and a Jacintha album. All are wonderful sounding and some of the best digital I have ever heard. If you have the DAC capable of playing DSD512 you would be doing yourself a favor trying some of these.
I have played these using straight Roon decoding and through HQPlayer. They are very close but I feel the HQPlayer playback engine is ever so slightly better. Of course Roon is the meta data/controlling software being used and feeding HQPlayer in my setup.