I use a Levinson 432 with my Cremona and it delivers 400 watts at 8 ohms and 800 watts at 4 ohms. Works fine. Based on my experience, he MC501 would not be to powerful. Based on my experience choosing amps for the Cremona, more power is better, but I have never tried MACs with them.
One thing to look at is the overall gain in the system. If the preamp and power amp together have a large gain, you end up using only a small portion of the volume control. My preamp can attenuate the input signal and I use that to give me more range on the volume control. So, I would check out the gain of the 2 MACs versus your Krell, just to be sure.
One thing to look at is the overall gain in the system. If the preamp and power amp together have a large gain, you end up using only a small portion of the volume control. My preamp can attenuate the input signal and I use that to give me more range on the volume control. So, I would check out the gain of the 2 MACs versus your Krell, just to be sure.