I originally had a 6GB HDD Sony shaped like a purple bean, and then I had a 4GB flash Sony with the most incredible sound quality. Building on the idea that this is the all out best that Sony can make, and that my iPod Classic sounds like flat New Coke tastes, I took the plunge and got an as new one off eBay.
The sound is stunning, although the detail comes at the expense of creating a little hiss during the silences. This is surprisingly not annoying, and is reminiscent of cassette Walkman. If the trade off for detail is a noise floor below the hiss generated by the hardware, then so be it. The Walkman also includes noise cancelling that will work with any headphones that incorporate a mic, and it also has a fantastic DSP and EQ that are actually worth using. The entirely digital amp is of such quality that external amping spoils the sound.
This is one of my most treasured possessions, and reading what Sony had to say about it, it looks like they intended this.
Pros: Audio Quality is excellent, solid build quality, nice screen
Cons: no FLAC or ALAC, pricey
Having owned a vast assortment of DAPs including Zune HD, iPod Touch 4G, Archos 604, 605, 5 IT, iRiver Clix, etc. This is definitely the best sounding DAP I have ever owned. The built in amp works extremely well with my UE11Pros to give crisp clean bass which is still quite strong straight out of the headphone jack. Mids and highs are clean and natural without any shrillness at high volume. I rarely go past the half way point on volume, the AMP is quite strong even without an additional amp.
Downside for me is the lack of FLAC support. However, I have learned the trick of using MediaMonkey to convert FLAC to WAV and that loads successfully to the Walkman in a lossless format.
The user interface is pretty good, although Zune and iPhone are better. The best thing about the user interface is that you can bring the display back up just by tapping on it, then the play button is easily accessible. There are dedicated buttons for play and volume control which I love -- something that is missing from most other touch screen DAPs.
The OLED display is bright, colorful, and crisp. Displays the album art very nicely.
Build construction is excellent, this is a solid unit that has some heft to it.
For pure sound quality, I would highly recommend the Walkman X even though the price is a bit on the high side -- you get what you pay for.