The Krell 400xi would be ok with smooth, laid-back speakers (usually with soft dome tweeters), like Spendor or Sonus Faber. Not even the ProAcs would sound good with it. If you use metal dome tweeters, you'll notice tilted-up high frequencies, which sounds like more detailed but induces listener's fatigue. Besides, according to Stereophile's test report, the heat sinks are undersized (if you play it loud), but I guess it's fine for normal listening. BAT doesn't have the typical "tube" sound, more analytical than smooth. Even the Integra (designed by BAT) home theater pre and multi-channel power sounds smoother. I like the MA6900, since I like to enjoy my music rather than chasing the absolute truth in recordings. Every piece of conductor in the path of music signals has a signature, even the electrical outlet in the wall (eventually I chose the FIM outlet for its warm sound). So my opinion is, choose the sound that you enjoy most, i.e. the amp that creates the most endorphin in your brain.
Krell 400xi vs. BAT VK-300x vs. McIntosh MA6900
I'm considering 1 of these 3 excellent Integrated Amplifiers to power my newly aquired Wilson Sophia Speakers. My Source Component will be either the Krell Standard or BAT VK-D5. Installing in a mid>large size living room. I'm looking for a smooth, full/robust, easy- on-the-ears sound. I'd rather not have to buy all 3 for an at home a/b/c audition, though I know that this is the preferred method of evaluating Components. Thought that I might give this post a try, to at least narrow it down to 2. Thanks!