I'm confused. The McIntosh 611 is a mono power amp, while the Luxman C900u is a pre-amp. Do you mean the M-900u, a two-channel amplifier than when bridged is a 600 w monaural amp, same rating as your 611?
In any event, the only Luxman product I auditioned recently was their L-507uX integrated amp, with a pair of Magico S1's. The sound was clear and uncolored, as neutral as one could wish if that is one's preference, with a noiseless background. I tried the amp at home with my less efficient, older Aerial Acoustics Model 8b speakers. It did not provide sufficient power and clipped at moderately high volumes. The L-507uX was listed as only 110w/channel at 8 ohms, 220w/ch at 4 ohms, compared to my old Levinson amp which is rated at 250w/ch into 8 ohms and 500w/ch into 4 ohms and handles my speakers without blinking. I cannot comment on the comparison of your McIntosh to the Luxman.
At 600 w I doubt you'll have any problems with the Luxman amp and expect you'd find the sound very lifelike with your Magico speakers. You might see if a dealer will let you demo the Luxman amp at your home if he has a demo he can loan and if you pay shipping both ways. Given the cost of the amp, it would seem worth asking. Note that the Luxman amp weighs 106 lbs without packaging. It will likely have to be shipped on a pallet in order to protect it properly.
Good luck.
In any event, the only Luxman product I auditioned recently was their L-507uX integrated amp, with a pair of Magico S1's. The sound was clear and uncolored, as neutral as one could wish if that is one's preference, with a noiseless background. I tried the amp at home with my less efficient, older Aerial Acoustics Model 8b speakers. It did not provide sufficient power and clipped at moderately high volumes. The L-507uX was listed as only 110w/channel at 8 ohms, 220w/ch at 4 ohms, compared to my old Levinson amp which is rated at 250w/ch into 8 ohms and 500w/ch into 4 ohms and handles my speakers without blinking. I cannot comment on the comparison of your McIntosh to the Luxman.
At 600 w I doubt you'll have any problems with the Luxman amp and expect you'd find the sound very lifelike with your Magico speakers. You might see if a dealer will let you demo the Luxman amp at your home if he has a demo he can loan and if you pay shipping both ways. Given the cost of the amp, it would seem worth asking. Note that the Luxman amp weighs 106 lbs without packaging. It will likely have to be shipped on a pallet in order to protect it properly.
Good luck.