Hm, I've got a 70s stereo amp and am not quite sure how I feel about it. I used it for quite awhile and got used to the sound, then I became surprised at how great my Denons sounded from my Galaxy S3 (almost better in a way, smoother). I think the output jacks of some receivers may be a bit too powerful for the Denons and aren't really doing the best for them. However, since my amp is in the shop at the moment, I can't do a proper comparison between the amp and a less powerful source. It's actually why I'm looking for a new headphone amp.
I was sceptical myself, but I've tried a number of amps and I keep coming back to my Carver. I've compared my setup side-by-side to everything from a DacMagic+Objective2 all the way up to a Violectric V800+V200 stack. Also had an Asgard, Peachtree Nova, NuForce Icon HD and never heard any improvement (or really any difference for that matter).
I bought my Carver new in 1985 and I've kept it all this time because it simply performs. I've bought and sold a number of amps over the years, but I have never heard anything than sounds better it in my home. Which isn't to say it's perfect, I once had a pair of Sennheiser HD 598's and the Carver was not a good match for it - presumably because of a higher than ideal output impedance. I wouldn't pair my Carver with any headphone that requires a high damping factor - (low impedance Senns, BA IEM's, etc.).