On McIntosh, Mac 601 doesn't sound like a 402 or set of 501s at all. This is like comparing Pass X250 to X250.5 imo. Totally different amps.
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That's a good point... my comments assume that the sonic differences between Pass and McIntosh would remain constant as one moves up the respective lines.
That said, having heard both the X250.5 and the MC601, what matching characteristics would you look for? Both are obviously high-current, high wattage SS designs, so presumably people would consider them for similar speakers (I tried out the X250.5 and MC402 as ~$4000 solutions for my Thiel 2.4s).