My experience is based on the 4004MkII, which I owned for a couple of years. In my system, I can easily hear differences in the amps I have owned. The 4004MKII was a bargin as discussed by others above. You could tell it was a sort of mid-fi SS amp (a little grain, fast but a little flat in the midrange) but its strength was that it sounded musical and did nothing really wrong. I upgraded to a Classe DR 25, which I thought was smoother, and displayed better dynamic range, and it can't touch my current McCormack DNA 500 for purity, power, midrange texture, HF decay, etc., but I would certainly like to own one again for my second system. IMO it kicks Adcom, Acurus, Rotel and others in its range. BTW, they are a great stepping stone since they are built very well and still sell used for the same price I paid 4-5 years ago.