I have owned the 4004, 4004mkII and I currently have an 8008BB - all Mondial versions(pre Klipsch). I have had friends help me A/B the 4004mkII and the 8008BB in my home, in my system on more than one model of speaker.
I can not reliably tell them apart soncially.
I have, however, been able to draw one decisive conclusion about these amps - the hotter you can get them, the better they sound.
Given that the 8008BB has 50% more output devices, more heat sink area, twice the capacitance and bigger toroids than the 4004mkII... it is easier to get the 4004 "hot".
If you have a really difficult load to drive, go for the 8008BB. If not, save some $$ and get a 4004mkII. I used my 4004mkII to primarily drive Carver Platinum Edition Amazings with 60 inch ribbons and four 12" woofs per side. These speakers have one of the nastier x-overs around to drive - dipping into the 1 ohm region in the bass. When the 4004mkII drove these speaks at high volumes, you could smell the paint on the lid.... and it never sounded better - :-)
I have never been able to get my 8008BB to even break a sweat no matter what its hooked to. I have however seen it smoke four 20 watt resistors wired in parallel in a crossover and not even strain doing it. In-other-words, this amp can deliver the "current" - I think you could weld with it.
I can not reliably tell them apart soncially.
I have, however, been able to draw one decisive conclusion about these amps - the hotter you can get them, the better they sound.
Given that the 8008BB has 50% more output devices, more heat sink area, twice the capacitance and bigger toroids than the 4004mkII... it is easier to get the 4004 "hot".
If you have a really difficult load to drive, go for the 8008BB. If not, save some $$ and get a 4004mkII. I used my 4004mkII to primarily drive Carver Platinum Edition Amazings with 60 inch ribbons and four 12" woofs per side. These speakers have one of the nastier x-overs around to drive - dipping into the 1 ohm region in the bass. When the 4004mkII drove these speaks at high volumes, you could smell the paint on the lid.... and it never sounded better - :-)
I have never been able to get my 8008BB to even break a sweat no matter what its hooked to. I have however seen it smoke four 20 watt resistors wired in parallel in a crossover and not even strain doing it. In-other-words, this amp can deliver the "current" - I think you could weld with it.