of the big amps I've heard the Krell was great. Didn't hear it with Proac speakers though. It was driving some 802 Matrix. I liked the Krell 600, MC602, and Linn 500 monos. For myself, I'd probably go with the Big Mac today as it's a current product.
Money being what it is though, and with Krells build, if it was a very good deal, I'd have little problem going with it then... but I'd have to have speakers which would really benefit from it. Otherwise I'd seek out a more manageable amp better suited to the speakers.
I heard the 250 monos on a pair of BW 801's. they sounded like they could use a lot more power than the 250s put out, although the 250s did come across as quite neutral. the 600 would have been a better match for the 801N's IMO.