What's wrong? Nuforce/Capri no better than Sunfire

Preface: this is regarding 2 channel analogue SQ.
OK. I know it's very early in the comparison process, and I've "only" critically listened for 2-3 hours. But whereas listening to speakers has shown clear differences (to a point), and the move up the B&W ladder from 9NTs to N803s was SIGNIFICANT, I'm at a loss on the amp/preamp. The jump from my old $4k Pioneer flagship HT rcvr to the Sunfire TGA5200 was very significant. Less significant but noticeable was the jump from the Pio as preamp to the Sunfire TGP5 as pre. I then read a lot about how a good 2 channel pre would crush an HT pre/pro. So I got the Jeff Rowland Capri. Have listened for quite some time and struggled mightily to justify the Capri, but I just don't hear ANY major improvement. Maybe some VERY subtle things, but I can't even be sure of that. I also read that a good 2 channel amp would crush a multi-channel amp. So I just picked up the Nuforce ref 9SEv2, and I've gone back and forth with the TGA5200, unscientifically, but again, I don't hear any major difference, whether through the Capri or the Sunfire TGP5. Am I just missing "golden ears" and reached the audio equivalent of the Peter Principal" (rising to my level of incompetence)? Is the Sunfire stuff just that good? Is the old claim that all good amps/preamps should sound similar true? It just strikes me as odd that so many people on these audio boards hear huge differences and I don't. What's wrong?