Krell fpb300/evo420e vs pass x350.5 any opinions?

Hi anyone to share his thoughts about these ?
I have a ps audio PWD mk2 liked to krell fpb300 and a wilson audio sasha on the end.I like the sound very much , but I am considering to change my amp with newer one .My list : krell evo402e , pass x350.5 ,pass x600.5 and maybe xa100.5?
I will appreciate any thoughts from people with exp with fpb300 and any of the above
What are you looking to improve from your current sound?

All the amplifiers listed above are fantastic. The Pass amps will not have the tremendous bottom end of the Krell amps (nobody does bass like Krell for that matter), but do other things a bit better IMO, especially the XA models.
i personally owned a Krell FPB-300 for awhile and liked it very much. it had a VERY slight
silvery top end, BUT it did not detract from the overall clean and 3-dimensional sound. the cosmetics were nice too- simple and elegant. but a friend had Pass Aleph amplifiers and they were a bit more organic sounding- a smoother top with no artifacts. we're talking small differences here, and for twice the price (retail).
the newest krell amp as well as the other newer amps are better than the alephs or FPB amps I have personally heard. but without very revealing speakers you're not going to hear huge differences amongst all these premium components.
I get the pass x350.5 from a dealer to evaluate - the unit was brand new and the first 4 days the krell (fpb 300) litterally blow it away,after that ( I still cannot understand how ) but for one day more the pass was obviosely betterered it- low end, midrange, highs - everything - more spatial info less or no fatigue at moderate levels ( the limit of the wilson) ,so I am continuing to burn it in - I will post another comment shortly
Oh and the difference is huge....
Will you evaluate the XA100.5s as well?
the dealer do not have the xa.100.5 in stock... too bad cause I wanted to compare it with x350.5 very badly..
So would I :(