Power/Current: How much is realistic?

I was always under the impression that it’s not really possible to overdrive speakers that require high current to drive

This is in need of correction- you can overdrive any speaker if you have enough power!

Now i just want to research options for class D

I would certainly give them a try. Class D is different from regular solid state- its artifacts are not the same. There can be difficulties with low impedances on account of the output filter of the amplifier; you'll have to check with the manufacturer on that. But the low impedance at high frequencies may not be much of an issue as there is not nearly as much power up high.

That should work just fine.

my mcintosh mc602's manual says it's current is 150 amperes per chanell. is this true

No. Not unless it can make well over 22,500 watts!! And that is giving it the benefit of the doubt- that it can drive 1 ohm.

@almarg I think ML specs their speakers the way they do because they are panels rather than point sources. In that regard a microphone placed 1 meter from the speaker will not pick up all the energy that the speaker radiates. If Stereophile measured it at 86 dB, 10 feet away from the speaker the sound pressure effectively is as if a point source were being used that is 5-6dB more efficient, so 91dB might be practically more accurate. This is why so many panel speakers seem crazy inefficient, but in reality aren't that hard to drive.