SACD: alas, seems on it's way out. Very few released being done this way now. With the vast majority of people listening to downloads or streaming on smart phones or worse, sound quality isn't important. And a well-done red book cd can stand up to sacd quite well. What is better is Blu Ray-A. Huge sound possibilities, unfortunately not being realized - and may never be. With the classical music market in near-collapse, and the record companies churning out big boxes from their large libraries, I wouldn't count on much. There's just not much interest in physical disks anymore - classical listeners excepted. And we're only 2-3% of the population.
The SACD format may not be seeing as many releases as before, but it seems still that runs of a particular album will be manufactured in that format if it is felt that sales will be brisk enough to justify the costs of manufacturing.
Downloads are certainly most prevalent in the popular music format, though it is best if a remastering of a given classical recording is available in a format higher than 16-bit 44.1-kHz format, which is no better than regular CD. Particularly if the recording was remastered in 24-bit, 96-kHz format, at least. The Kubelik and Gergiev complete Mahler cycles are the only ones I'm aware of, that are available at HDTracks.com, though I haven't downloaded either of those. The one recording I've downloaded from them that I felt was worth every penny I paid was EMI's Klemperer Brahms Requiem, and that remastering has finally eliminated the distortion that was evident in all previous releases of that recording, LP, tape, or CD. Many of the famous RCA Reiner and Munch Red Seal recordings have become available from HDTracks in 24-bit, 176-kHz format. Those will produce files that are quite large. One thing that's important to realize before downloading 24-bit recordings is to make sure that your equipment (other than a computer connected to a room stereo system as opposed to desktop speakers) is able to play 24-bit files. Most CD players cannot play 24-bit mastered sound files, only 16-bit. HDTracks does provide a sample 24-bit file that you can download to see if your equipment is able to play 24-bit files. A universal-format disk player is generally the only type that can do this, provided the circuitry has been pre-programmed to play 24-bit files, be they via a flash drive, memory stick, or DVD disk.
As far as Blu-ray audio is concerned, the record manufactures have been abysmally SLOW in producing recordings in that format. Virtually all of the ones available are remasterings by Universal from the Decca, DG, and Philips analogue catalogue, of which the Mehta M2 and Solti M8 are the only Mahler ones available.
Wade
