[quote author="Osse"] could anyone explain how the discrete one works, and what the sound difference compared to IC opamp is, if there is any 'general' sound difference.[/quote]
The first opamps were very 'discrete" indeed (although their failures were not necessarily discreet :grin
. They used tubes, rarely had a noninverting input, and had a lot of drawbacks.
With the advent of sand state we started making reasonably small modules with discrete transistors inside, along with supporting resistors, capacitors, and sometimes diodes. At the same time monolithic fabrication of arrays of devices was in intense development, leading to some workable but generally inferior-performance integrated-circuit operational amplifiers. But the appeal of miniaturization and cost reduction was compelling for a lot of applications.
The circuit topologies (the way that parts are connected) derived from discrete opamps were applied pretty much directly at first. Then various brilliant people began to think outside the box and realize what could be done with monolithic structures. It was said that Bob Widlar bedeviled the drafting staffs he worked with, by forcing them to come up with symbols for devices that didn't exist as discretes.
At this time the circuit topologies began to significantly diverge. Of course the principles of operation of transistors and so forth didn't change, nor have they to this day, so the basic answer to your first question is, both IC and discrete amps work the same way.
Now, to the second point, we enter into the fuzzy realm of subjective evaluation and to what extent measurements correlate with sonic preferences. A very simple discrete design is apt to underperform a well-designed integrated part as far as our measurement tools reveal. Sometimes the higher distortion and other coloration may be perceived as desirable. Sometimes not.