"Anybody know if the next-gen video discs will have better audio than currently available on DVD-A or SACD?
Not until movie studios upgrade from 48khz recording. DolbyTrueHD uses an improved version of the Dvd-A mlp codec.If you google the 2 formats home pages they will probably explain whats possible ( Bluray are particularly good at speculation but it will be some time before > than Dvd-A/sacd sound is available IMO.
For PCM, the 192khz/24bit format is currently the highest resolution being used in recording studios, but that is a very rare occurance - 96kHz/24bit is much more prevalent but relatively speaking even that is rare compared to the 44.1kHz and 48kHz recording formats. FYI: there are many respected professionals who scoff at using anything more than 96/24.......and sometimes 48/24.
DSD: IIRC there are higher recording resolutions available than what's built into all sacd players (there is only one DSD resolution for home players & and that is the 2.8mHz/1bit format), but I don't know if such formats are backwards compatible with existing sacd players (PCM can be easily downconverted in a player to lower resolutions).
DVD-A and SACD didn't get much publicity... so i doubt we will see BR+HD-DVD music only anytime soon. it is technically possible... but in terms of market viability, i doubt it. as lance brought up, CD's 44.1 pretty much takes care of MOST of the recordings we have today and for the foreseeable future.
on the other hand if BR+HD formats catch on close to SD-DVD's craze... then music on these formats will just be a BONUS =). gravy.