Well, here is my story. I used to drive my speakers from AVR initially about for a year. I am very sensitive to harsh treble & sibilance. I used to cringe when I heard some of my favorite recordings ruined by sibilance. Eventually I completely stopped listening to some of them. Later I read somewhere that AVRs sometimes clip slightly introducing some harmonics which are heard as sibilance and harsh treble. So, I got a 2 ch power amp using my AVR's as DAC + preamp. There were some improvements, but not too much.
Just a month back I thought of replacing my 200 rupee RCA cable with a nice pair of nice interconnects not expecting much change in SQ. I was very doubtful that cables can sound good/bad, but still wanted give a try. So I gifted myself a pair of nice interconnects (Audio Art IC3 -- thank you Sridhar!) on my birthday. Reason: any other day I couldn't convince my wife to spend 4k on a pair of wires that too 1/2 m in length. (Okay, she agreed after I lied to her saying it was solid silver

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At first it just blew me away! Then again, and again, and again... Frankly I couldn't believe my ears! I mean it was like listening to a very high end system after a good dose of grass

Results were THAT good -- bass, mid, treble -- they were just flowing. Immediate difference I noticed was that sibilance was totally gone -- without any loss in treble detail and extension. I never thought I would write about ICs making a difference in sound, but here I am.
Now that I am out of that initial WOW period, I am beginning to think it could be that my power amp's muscle/finesse was not completely used with a cheap interconnect. May be, may be not but the combo definitely did.