Ok, this is it. I want to decide between two three used amps.
1) Musical Fidelity A3CR Dual integrated Mono Amp: Gets extremely positive user and pro reviews.
2) Van Alstine Omega III 400 (one year warranty): Components and design seem excellent, but I can't find any comments or reviews about it.
3) Parasound Halo A23
Thank you everyone for your kind help.