w/r/t damping factors: Marsh = 800, Sim = 800, Plinius - no data found. w/r/t output: Marsh is 200w @ 8 ohms, 330 @ 4 ohms; Sim is 120 @ 8 ohms, 200 @ 4 ohms, Plinius is 100 @ 8 ohms, 160 @ 4 ohms. w/r/t THD: Marsh = .02, Sim = .01; Plinius = .05. S/N on all are 100db All data from respective manufacturers websites; reviewers and your numbers may vary (and do: TAS said their test on the Sim W-3 showed a damping factor that "never went below 500"; but as mentioned above, at over 100 it's probably academic.)
I would like further explanation of the statement "A properly designed amplifier will not interact with the speakers." I always thought it was that very interaction that dominated the resultant sound from the system: spend all the money in the world on your front end and speakers, it'll still sound like mush thru a $120 integrated from Best Buys. Which is not to say other components don't get their signature into the mix, it's just that clean power delivered to well matched speakers will better enable you to hear everything that's happening in the system (and therefore, from the source, which is what we want to hear in the first place).
Don't rightly know where Plinius products are built, nor Sim, nor do I particularly care - it's sound and specs that speak to me. Especially sound.
chas