Hi there,
I have owned the KAV300CD, then the SACD Standard Mk2, which I recently had upgraded to Mk 3. A year or so ago I also had the DVD Standard on loan for a few weeks while the SACD went for repair.
The KAV300CD was rather 'dark' sounding, but had the Krell trademark slam and punchiness. The SACD Standard had much more extension in the highs, better transparency and greater resolution. The trade-off was a more polite presentation with less punch. Overall though, a great improvement.
The DVD Standard regained some of the punchiness of the KAV300CD, it almost matched the resolution of the SACD Standard, but was not so transparent and refined as the latter. For instance, female vocals lost some delicacy and intimacy.
However it does has gorgeous video output, so if you want both audio and video, and are prepared to sacrifice a little refinement in the audio to have fantastic video, then the DVD Standard would be a good choice.
If purely for music playback, then SACD Standard will be more satisfying.
The SACD Standard Mk3 is on a completely new level. It is supremely resolving, refined, and nuanced, yet it has slam, punch and pace. A very high end player. I can't recommend it highly enough.
Buy a used Mk2, and get Krell to upgrade it to Mk3 for you.
The upgrade has been discussed here:
http://forum.audiogon.com/cgi-bin/fr.pl?ddgtl&1202312587&openflup&12&Expensive, but absolutely worth every cent IMHO.
Cheers
Mick