The original 250cd had a very cheap and noisy Sanyo transport mechanism that gained quite a reputation for bad tracking. My suggestion is to stay away from this model. I had one for a few months and had nothing but trouble with it(not reading and/or skipping tracks of discs I never had any problems with before).
Although looking almost exactly identical, internally the 250cd/2 is very different from the original 250cd. For one thing the transport was a much better unit sourced from Philips (I don't remember the exact CDM modelnumber), while the analog circuitry was upgraded to Krell's Current Mode technology similar to the circuitry used in the 300cd. Consequently the 250cd/2 was about $1k more expensive than the 250cd, which in turn instigated a similar price increase of the 300cd. It has only been in production for a very short period of time, before Krell revamped the KAV-line and introduced the 280cd.
The 300cd is a rather more substantial unit fitted with a TEAC VRDS transport mechanism. I have used the 300cd for a couple of years and can vouche for its reliability.
All three units share the same Burr Brown PCM-1704 DAC chips (one per channel in each case) as well as the ubiquitous PMD-100 HDCD filter chip.
Soundwise I have compared the original 250cd and the 300cd and I would say that although they have a similar sound balance, the 300cd has substantially more (and better) bass as well as a more refined and extended treble. But probably due to the Teac transport the 300cd has a more measured and relaxed performance, rhythmically perhaps a bit on the slow side. The 250cd was lighter on its feet, but rhythmically also rather confused and unsettled.
Although I haven't heard it, from what I've read the 250cd/2 might just be the best choice of these three players, combining the premium digital and analog circuitry of the 300cd with the rhythmic agility of the Philips transport.
Although there are better cd players around today, for the price they now cost on the used market, both the 250cd/2 and the 300cd offer good value IMHO. The 300cd has been longer in production and therefore should be easier to find. Due to the complete restyling of the KAV range you can even find new units for very low prices. In case of a new unit, let it cook for at least a weeks on constant repeat before passing any judgment. These things sure take their sweet time to burn in properly.
Hope this helps.
cheers,
hans
