Why doesn't the specialist like the HK amp?
Because he wants to push Yamaha and Arcam
I have limited experience of HK's - a friend bought a AVR335 some time ago, but I would suppose that compared to most Denons, Yamahas, Pioneers and Onkyos it would appear that the HK's power is understated as most of the other brands do not specify their power ratings with all channels driven whereas HK is fairly conservative and specify the ratings with all channels driven simultaneously.
Personally I was not really impressed with my friend's HK and we both felt that it did not have the power and drive of the CA(Stereo mode), but then again the HK 335 is rated much lower in quoted power delivery(all channels driven). The sonic signature did not appeal to me either, but that's a personal preference and no reflection on the quality of HK.
We went a step further and did a side-by-side comparison(Stereo mode) with a Yamaha RX-V650, Denon 2805 and a Pioneer VSX1015(other friends kindly supplied them

) and in this case the HK outperformed them in power delivery.
So what I am trying to say? Is CA better than HK and HK better than Denon, Yamaha, Pioneer? Not at all, only that HK's as the others mentioned are quality products, but YOU have to decide which one satisfies your needs and don't base your decision on quoted power ratings
