A room where the sound doesnt reflect off the ceiling, floor, or walls. The size of the listening area doesn't matter so long as you have enough power to fill it adequately. You will have to watch for nodes and nulls, and other such problems in any room, unless it is acoustically treated.
Anechoic chamber would be ideal, but you're forgetting one thing - bass. Anechoic cahmbers don't reflect enough sound for bass to be proportionately present, so I've heard.
Wahl - I don't think this quesation can really be answered.
The ideal would depend on more variables than I have time at lunch here to list. Let it suffice to say that we would need a whole lot more info than you have given us to answer that question.
