FPB 750mcx OR EVO 402e

I think the FPB series is phenomenal. Look at hificritic.com Martin Colloms website...he ranks both and the ranking is very close despite the years that separate these two. Some have said the 750mcx is one of the finest amps Krell ever made...and with depreciation you'll get a great price. And then you'll never wish you had more power! I have never heard it...but know people who've owned, it heard, and i understand it is more refined than the FPB600 monos and surprisingly close to the current reference Krell Evo Ones.

If it were me I wouldn't do it!!!!!!
The 400 is not even in the same boat....all I have read is subtle differences and not worth the extra $$$$$$$$$$$$$
just my 2 cents