I had the Krell 300i which I used with Dunlavy SC-III's for years. I always enjoyed it. Last year I got a Primaluna Prologue 1. Since that time I haven't hooked up the Krell. The PL is much more musical, bigger more 3 dimensional soundstage, more natural sounding. The mids are incredible with the PL when compared to the Krell. I am hearing things in the mids I never heard with the Krell. The only thing I lost was a slight amount of bass punch. I have never heard the 400xi and it may be completely different from the 300i so my experiences may be pointless for you. I thought I'd throw my experience here since you are a Dunlavy owner in case it helps.