alexatpos, thank you for relating your experience in regard to Schroeder Method and your system. Every contribution to understanding it is helpful. I wonder if the output of the CD player is a factor in the outcome you experienced. There is a possibility that the capacitance of the doubled interconnects was too high.
One thing that is very helpful in the overall assessment of the doubling of ICs is that it seemed obvious to you that the sound had changed. That in itself is important, because it reinforces the experience of others, that the sound changed noticeably.
It would be helpful to me and the community if you would share the precise make and model of your CD player, Preamp and Amp so that the specifications could be found, and perhaps better understanding of what might be the issue can be discovered.
I wonder if you are using a very low power amp and if that might be a factor in the result. I had discussed use of double ICs with Kevin Hayes of VAC and he said it would present no problem with his amplifiers. But, I hasten to add that the topology of amps, even tube amps, can vary dramatically, so this response certainly cannot be extended to all amplifiers.
Again, if we can see the equipment used that would be very helpful to everyone.