Krell KAV400 VS Musical Fidelity A300 A 3.2 A3.5

The difference is clear if you listen to them. Both have their adherents. I would highly recommend listening to both to see which sound you like. Krell - forward, detailed, unforgiving. You'd better have a good source because the Krell will let you know every flaw. MF - warmer sounding but not exactly the tube warmth but it seems they're designed to have some sort of "presence." Rounder, somewhat fuller. The highs can be just as etchy as the Krell but are somewhat covered by the fuller lower end.
If you have a great, and I mean really good, digital source and don't listen to a lot of boosted, compressed music then I'd go with the Krell. Otherwise if you want something more forgiving the MF.

I listen to LPs exclusively. Dos it mean I better go with more forgiving MF?

Unforgiving is another of those words poorly used to describe audio. It means nothing. If it is intended to mean that it reveals nuances in the performance of components upstream in the system, then that is how it should be termed.

As I said earlier, I own both of these amps and have immediate and present experience with both, in my home, in my system. To me, the Krell presents a less colored version of the recorded performance than does the MF. The MF has what I hear as a mid bass bump that adds what some might term "warmth." My personal preference is to hear recordings the way they turned out, and to able to separate the "wheat from the chaff." Many recordings do not sound good primarily because they were poorly produced. The last thing I want is a system that artificially colors the music in a way that does not let me hear it as intended, for better or worse. Others may desire such artifical coloring to try and "hide" blemished production values and I respect that. To me, such an approach eventually becomes fatiguing. But the Krell is no more "forgiving" of music than the MF, which simply colors it more so as to provide what I perceive as artificial warmth in this quite audible portion of the frequency spectrum. Some may desire this.

By the way I listen to vinyl 50% of the time and have an EAR834P phono pre that "warms" up the vinyl presentation. Again the Krell provides an "auditory view" into this setup that is accurate; I wouldn't have it any other way.

Also I listen to jazz, rock, classical, electronica and I have always maintained that any system should be able to play back all styles equally well. Otherwise there is something askance and will eventually lead to disatisfaction.

To each his own. I spent a lot of time and money on "revealing", "nuanced", "accurate", "detailed", and the coda: a quote from The Matrix: "You know, I know this steak doesn't exist. I know that when I put it in my mouth, the Matrix is telling my brain that it is juicy and delicious. After nine years, you know what I realize? [Takes a bite of steak] Ignorance is bliss." I concluded I like what sounded good over what really was 8 days a week.

I have never owned either, but one Minor point.
The Krell runs pretty warm...hot even. I listened for about an hour at the local emporium. The Krell was hooked to Magnepan 3.6r speakers, 4ohm and I don't know how bad an actual load. Within 20 minutes, the Krell was cookin'.

If you DO get the Krell make sure you have a Well Ventilated space.