Hi there - saw this interesting thread and i thought i would add my bit...
I have used Akai samplers for 11 years, and there is indeed a sound quality difference with every one i've used.
The main reason for this is because of the analogue input stage. Although the converters in early models were not as highly specified as they are today, there was a significantly more amount of analoge components. This was because, early on in the days of digital sampling, the converter chip was just an A to D converter.
As we have progressed down the digital road, it has been possible to put more and more processing 'on chip' (this is cheaper to make) and so less analogue components are used, resulting in a more clinical sound.
When i first got my S3000 way back, i nearly took it back to the store - it sounded so different from the S1100 - much thinner. After exchanging samples, and doing a load of tests, thats the conclusion we came to at the time.
The same is true of the old Roland S series. A sample made in the S750 or S770 sounds way better than the S760, but when the samples are exchanged, we could hear no difference
This is not to say the qulity is poor, it is just missing the warmth of the analogue input stage, and is easily overcome (and improved) by recording signals in through a FET amplifier like what is used in Urie 1176 and Universal audio products.
Its strange that, as converters have increased in quality, it is the analgue stage that really seems to make a difference.
In my opinion as a sound engineer, the best non-valve analogue sound you can get it the planet is his:
http://www.uaudio.com/products/analog/2-1176/index.html
(but it costs $$$$!)
Maybe try renting one for a while - then you will know what i'm taking about.
I hope this helps.
