The Orangutan is intended to be moderately high efficiency and an easy load for tube amplifiers. A transistor amplifier is not likely to show them off properly- I suspect that the design may not work properly with transistors. (for more on why, see http://www.atma-sphere.com/Resources/Paradigms_in_Amplifier_Design.php.)
Given what I have seen of them, to really make them sing you will want some power, of course a lot depends on your room!
Given what I have seen of them, to really make them sing you will want some power, of course a lot depends on your room!