OK, the baby is asleep (for now), so I'm going to write as much as I can until she wakes up.
First of all, IMHO the 'golden era' for Sony ES players was the mid-late 80's up to the early 90's. That's largely based on build quality observations but also my personal preference is for the older multi-bit DAC chips, which I tend to prefer. After the early 80's the mechanical build quality tailed off a bit, especially that of the laser mechs.
Sony ES CD players from the era that I'm interested in can be roughly divided into three groups:
1) Philips TDA1541 based players
2) Burr Brown DAC chip based players
3) Sony DAC chip based players
The above is also my (approximate) personal order of preference as far as the DAC chips go but the DAC chip is just one facet of what makes a CD player good/bad and I'd much rather have a top of the range player with a Sony DAC than the cheapest player with a TDA1541 DAC. Implementation is at least as important as the DAC chip.
Sony made/make everything from cheap and nasty junk right up to stuff that is just incredible quality that can put even the most exotic kit to shame. The best analogy I can think of is in the car industry were Volkswagen Audi Group (VAG) own Skoda, Seat, VW, Audi, Porsche, Bentley, Lamborghini and Bugatti. Now try and imagine that ALL of the cars that VAG make were all branded Volkswagen and you get some idea of the variance in the quality of Sony kit! ES stands for Elevated Standard and roughly divides the Sony range into two parts. Imagine VAG only had the VW and Audi brands to cover their full range and you get the idea.
The Sony model numbering system is totally baffling and sometimes I think they just used a random number generator but approximately speaking a higher number within the ES series indicates a superior model and/or a later model. So, for example the 337 is superior to, and came out after, the 333 and the successor to the 337 was the 338. It's is however important to appreciate that newer certainly doesn't always mean better and there are a lot of cases in which the earlier model is superior! The 2xx range is roughly lower in hierarchy than the 3xx range, which is lower than the 5xx range and the 7xx range are top models. However, there are many anomalies and 'gotchas'. For example the 555esd and 557esd are some of the very best ever despite not being in the 7xx range.
Non ES models do not equate! For example, a CDP-597 is worlds away in quality from an ES CDP-557ESD model.
I've got to go now. More later.....