Anyone hoping for a true DVD-A digital quad mix for King Arthur or Six Wives is in for some disappointment. While the DVDs are hybrid, including MLP lossless, Dolby Digital and DTS, the quad mixes included are clearly and audibly sourced from needle drops of old quad vinyl releases. As such, rumble, surface noise and repeating defects mar the listening experience, particularly in silent or quiet passages. King Arthur is the worst for this, especially on Guinevere. At about 40 seconds in we are treated to 12 seconds of nothing but turntable rumble and surface noise. Also Merlin has many audible repeating defects especially at the beginning. In contrast, the Six Wives vinyl seems to have been in much better shape and the background noise though frequently audible is not nearly as intrusive. I've also noticed that the sound level on the King Arthur DVD is much lower than on the Six Wives.
As to the quad mixes themselves, probably not surprisingly Six Wives is much better, allowing the listener to clearly hear the different types of keyboards and other instruments being played. In particular, the mellotron comes through much more prominently. Alas for King Arthur, in quad the vocals (which were already quite weak and annoying) are mixed horribly, sounding both muffled, compressed, and unfortunately more prominent. At least for me, King Arthur was a major step down in quality for Rick Wakeman and the quad mix does not help. If anything, it reveals how simplistic and cheesy most the music is. Only Merlin and parts of Guinevere and The Last Battle even approach the quality of any track on Six Wives. For anyone with a sound system offering a variety of surround processing modes, I got the best results by turning additional processing off and just going direct.
There are also MLP lossless stereo versions included on both DVDs. It's unclear if these are sourced from the new remasters or not, but they do sound very good with one exception. On King Arthur, the piano intro to Guinevere is marred by a warbling, echoey distortion which disappears at the 50 second mark.
For me, the Six Wives Deluxe is definitely worth recommending as a purchase. The stereo remaster offers an audible improvement, and the quad mix is interesting and revealing even if not essential. It's also easily Rick Wakeman's best solo record and this is likely the best we're ever going to hear it. However, after listening to the King Arthur I wouldn't recommend it to anyone except die hard fans or completists.