In the case of the pioneer it's 24/96 for DVD audio (not to be confused with DVD-A, but rather DVD video standard that is an audio disc only--some companies refer to them as DADs). These discs have the audio in 24/96 format and if you select the output on the pioneer for that it outputs at 24/96. CD's are still ouptput at their standard (redbook) output. The pioneer is not doing a resampling for you on those discs. So the advantages are for a limited set of software, and as you point out you need a 24/96 DAC to take advantage of this digital output.
true 24/96 digital output
in many of these threads, use of dvd or cd player / changers as transports are discussed, but it doesn't seem anyone has addressed the advantages of true 24/96 output. i've read that cheap pioneer dvd players have 24/96 digital output. is this advantageous in use as a transport? if your software is a regular cd, it's likely recored at a lower rate, so is the advantage only limited to certain software? this is, of course, assuming an outboard dac that desinged for a true 24/96 signal...