Krell FPB 600 or 250M's?

The only difference (I'm told by Patrick at Krell) between the mc and mcx line is "cast", that's it. If you are not using cast (other than Aesthetics) a mc and a mcx are the same amp. 
Krell and most reputable High-end brands work really hard to have "a brand type" and furthermore a "line or model type". This would not exclude a certain sonic signature that you should expect out out of a model line. A 250mc should have the same sonic signature as a 750mc.
As a current owner of 8 Krell amplifies and the previous owner of dozens before this is what I found this to be true. 
I can't speak on modified amps as I have never owned one, most manufactures don't recommend it, and I'm a bit of a purest to the to the original engineer's design philosophy.
Of course weather YOU like a line/model personality is subjective, what blows someone else away might only be meh to you.  

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doug2507, do what you like,  my opinion is the 600 over the 250m, cheers 

Strych2, I agree with you on the mono-block is better,  shorter speaker cable's,  however,  to be clear,  the 250 m is bright sounding with most high quality revealing cable's,  where the 600c or 700 is extremely better in every way with any cable's,  the only thing that would beat this out is 650m or 750mcx,  as a matter of fact,  the 700cx is better than the 650m!, the cx line is a total different animal in sound than the original or c model's of the fpb line,  I know, I have owned many, and my ride off into the sunset amplifier is the only krell modified 700cx anywhere,  I spent  $11,000.00 with up grades that will blow a stock 750mcx out of the water 😎

I agree with Kirk930, I have owned all of the FPB series. Other than space and price ( fpb 200 vs 250) Mono blocks are the way to go! Separate power supply to each speaker and shorter cable run for less interference (are just a couple of the benefits). The best speaker cable is no speaker cable at all. So by shortening your cable run to Below 1m has neat benefits. Last but not least there is zero stereo cross talk.  
  

Just ran across this thread. I must disagree. I think the 250 monos would be a much better choice. The 600 may have more power but not even close on everything else.

Speakers matching with the fpb isnt really a problem. From what i gather the FPB has quite a smooth upper range so shouldn't be too fatiguing with the proacs. Add a tube pre into the equation and everything should be fine i reckon. I know the proacs work best with tubes but i still like the punch and speed of SS so a tube pre should be 'enough'. Source is a KPS20i(delta 9).

I'm inclined to go with the 600 as well. From what i can gather it really is one of the all time greats and a keeper. Mono's mean more boxes, more heat, more cables, more cash if they go wrong. Just wandered if they were even remotely in the same league as the 650's which would probably be the next step up from a 600.

Buy the FPB 600/700c. I have one I bought new in 1999 and it has dusted everything that has gone up against it driving Thiel CS5i's and various Apogees, both brutal loads. The tonal weight, richness, and dynamics of this amp will keep you smiling for many years to come.

It does get VERY hot and requires a minimum of a 20 amp dedicated line (30 amp is better), so keep that in mind.

FWIW...

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.