I am really happy with MC18 and the sound quality it produces, outside of technology upgrades and options, will MC21 produce a noticeable difference in sound quality over the previous version?
Just my observation on this type of thing...
I read CONSTANTLY on another forum about a certain Mac audio player that claims audio improvements with each new version. People there fall all over themselves asking how the new one sounds and occasionally ask what the new sound quality is based upon. I have yet to read ANYTHING technical about the claims of better sound quality. In that particular forum, about that particular player.
I have to ask myself, how many improvements can a proper digital audio player make? This isn't an analog product. You can't use new speakers to make better sound. You can't lower the noise floor by using higher quality power supplies or better components. You can't improve linearity by using a (more) properly biased amplifier stage. You can't improve high frequency response by reducing inductance.
My point is that, with other parts of the audio reproduction chain, you can address specific things to improve, or at least change, the way things measure and sound. With a *software* player, there are definitely things to be done to do it correctly. But once you get beyond the correct basics, what more can you do? I think the basics of digital audio are pretty well understood by most companies that make good players. Perhaps there's something here I don't know though. <shrug>
Players that claim to increase sound quality over and over make me skeptical. They remind me of things like "magic pebbles", green pens (for CDs), cable stands (to hold them off the floor), multi-thousand dollar speaker cables, and the like. In short, I think they are probably straight up lying.
Oh and for your enjoyment if you haven't yet seen it. One of the most technically advanced audio improvements available. The Teleportation Tweak:
http://www.machinadynamica.com/machina60.htm(I think the link above is absolute BS, but it's fun to read. Also fun to ask how many people have purchased this "product".)
Brian.