Sony MP3 new/used good-better-best?

In order of SQ from the models I've owned:

1. Sony X

2. A829

3. S639

4. A808

5. S706

Numbers 2 to 5 are fairly close from an enjoyability point of view, but the gap between the X and the others is quite substantial (to my ears )

But that doesn't mean the others sound bad, they don't. It's just the X takes everything one step further

I know this isn't quite the answer you are looking for but I upgraded my fuze to an X yesterday and the difference is very noticible, the fuze sounds great but the X, as soozie said, is a clear step up (I sent a Cowon D2+ back because I didn't feel it offered anything over the fuze but the X is a keeper for sure)

Hey. I've owned and still own a sony nwz-s639 which is still supposed to be one of the best-sounding sony to date and just got a fuze recently for cheap on ebay... And, well, i would say none sound better than the other. I like the sound of the sony better un-eqed (less flat, a little more bass and treble, slight v-shape, closer to my preference) with my px100 but i like the sound of the fuze (un-eqd) better with my pl21. The main difference is the sony has a much better EQ that i actually use quite a lot (and clearbass is great to get that bit of extra sub-bass when you feel like it), whereas the fuze eq is just useless.
So i would say that if you want to improve the sound you're getting or just want to hear a different sound-signature, i'd rather advise you to get another pair of phones instead (or rockbox the fuze if you'Re lucky to have a v1).
That being said, the UI of the sony is 99999999999 times better than the fuze's, and the screen quality also (i dont watch videos on none of those but i can enjoy watching the albums covers on the sony with great detail and clarity, whereas on the fuze they just look like a small ugly pack of big colored pixels mashed together)

in order for me:

S639
A829
A808

i haven't tried the X series yet

My klipsch S2's which are Klipsch's cheapest IEM's sound absolutley amazing with the X.

Cheers

SQ wize, i do not think the sony is that much of un upgrade over the fuze. I do tend to like its sound just a little better un-eqd, but sonically its main advantage is a quite good EQ which can make a LOT of difference (i hope you dont use the Fuze eq!)

Other than that here are its main advantages over the fuze

-much better screen with much better definition (=more info displayed on the screen, really perfect looking artwork even in thumbnails)
-much much better user interface, which makes it way easyer and intuitive to navigate through your music and have the info you want displayed before your eyes at the right time (i thought the scrolling wheel would be an advantage, turns out its not). Also the UI is much more responsive (NO latency when skipping songs), making you forget there is a software (firmware) between you and the hardware. Also the firmware is rock-stable.
-also much prettier user interface with nice themes/skins, which i think tend to affect the listening experience (how ugly is the fuze UI, really)
-MUCH longer battery life

CONS
-Impossible to delete a given song directly from the player, you have to do it from your computer. This is retarded since its possible to delete videos...why not songs? Why sony, WHY???
-Impossible to create playlists on-the-fly (at least with the fuze you have the go list which is pretty limited, but still)
-Format support limited to mp3, wma and wav (also atrac3 i think), vs the mp3,wma,ogg,flac,wav(and more?) of the Fuze.

And here is the other main advantage of the fuze, that you already know about : expandable memory with microsd!! Dont forget that 32gb microsdhc cards will soon be available!

EDIT: another advantage of the fuze vs the sonys that i had forgotten: RATINGS (which proves useful even though it could be much better implemented)

I had a totally different aural experience to you with the Fuze and the X

Much as I liked my Fuze as a great value-for-money and easy-to-use dap, it didn't compare at all with the X. The Fuze soundstage was much smaller for a start, and at louder volumes it didn't handle busy tracks as effortlessly as the X, (which hardly breaks a sweat no matter what volume I use).

Price wise though, the Fuze can't be beaten. I had an 8GB model with 16GB card for less than £100. The extra 8GB of the X cost another £180 on top of that... but it was totally worth it to me. I saw it as a huge upgrade in sound quality over the Fuze - but the Fuze is still a very good dap. I just think the X is much more open, musical, and way more detailed.

I think daouda was comparing s-series (S639?) with Fuze.

^^yeah, forgot to mention i was only talking about the sony s639 (which i own) that OP thought about purchasing, i don't own and never have heard the X.
If you thought i was talking about the X this leads me to think it's still impossible to delete songs directly on the player nor is it possible to create playlists on the fly with that later player.... It'S sad that sony doesnt consider expanding its firmware functionalities with newer models!

Oh dear, that will teach me to read more carefully!!

Mind you, I still preferred my 808 and 639 to the Fuze, but not by so wide a margin.

I know this is off the tangent, but all the higher-end Sony walkman's have this feature Sony calls "Clear Stereo", which they describe as:

"The Clear Stereo function enables individual left and right digital processing of the sound. This prevents audio signals leakage so that clear stereo sound of the original source can be reproduced."

This sounds to me like the presence of dual DACs or something similar. Anyone have any opinions on this? Does every A/S/X series Walkman actually have two DAC's hidden inside?

(I personally find the setting increases stereo seperation and soundstage, but recesses vocals a little and might have a little effect on detail on my RE0...)

And I own a Sony A806 and a S739, and found that the A was slightly warmer but the S was cleaner and with slightly better bass. The differences were very marginal however.

Sorry. Yes, I thought you were talking about the X. No, you can't delete audio tracks from it, just video. I always forget what I want to delete by the time it's plugged into the laptop

No on-the-fly playlists either. Lots of features got dropped after Atrac/SS was dumped. But I really cannot fathom why Sony didn't implement one for its higher-end model. Much lesser daps have playlist functionality. I'm not greedy. I'd settle for just one!