Couple of quick comments then need to get back to the lab and swear at a SerDes for a while...
- As has been said, a single sample, while not an ideal infinite-bandwidth impulse, represents the limit for a sampled system and is a common test for stability, frequency and time response, etc. A sampled system uses the zero-order hold math rather than analog impulse but the results are similar and the single-pulse sample tells how the system handles its maximum bandwidth input.
- Back to the original question, I (and I think most of us including Amir) acknowledge the biggest amplifier performance metrics influencing audible changes are likely to be noise floor (hum and hiss, mainly for high-sensitivity speakers) and output impedance. The latter is IME/IMO most likely to explain audible differences among amplifiers operated below clipping (and above the noise floor, natch). That is the load issue discussed many times in many threads (including this one).