A lot of you folks who are talking about running Krell amps into MLs over the years are missing one obvious (but critical) point in this discussion: The KAV series is NOT "your daddy's Krell" (to paraphrase an old Oldsmobile commercial).
Krell admits on their website that these little integrated amps are NOT the massive current powerhouses that their stand-alone amps have traditionall been, and just about anyone who owns hard-to-drive speakers has found this out.
I have a KAV-300i, and although it will drive my Sequels, it starts to run out of steam at about the 4th LED on the volume control. I'm currently using it as a preamp, and in that function it does FANTASTIC.
So while the KAV integrateds might be rated for 150+wpc, these are NOT the "same sort of watts" that you'd get from a KSA, KST, or FPB. The KAV line havepittifully small power supplies (well, small by Krell standards) and they just don't have the ability to deliver those massive transients like the bigger Krell stand-alone units...
If you're driving some stylish 8ohm minimonitors (Sonus, Gallo, etc) the KAV integrateds can sound REALLY sweet. But expecting them to drive something as outrageously demanding as a ML Sequel (or Sequel II which what I think you said you had) is just asking too much from this little integrated amp. You have to remember that Krell is not really marketing the KAV line toward "audiophiles" as much as they are trying to use this line (with it's clean design, rounded corners, and simple, smallish front panels) to make Audio "cool" again--like "hifi" was in the heyday of the '70s and 80's. They are obviously aiming at a VERY high SAF with the slimline components, silver faceplates and jewel-like buttons and displays. The whole KAV line is aimed at the upper-middle-class suburban demographic--people who aren't necessarily audiophiles, but might be driving a Beemer or their first Benz, and are worried about how the yard looks in front of their $1million "McMansion" in the 'burbs. People who think they need to impress someone with their STUFF, who need to proove that, in fact, the current generatio of Americans ARE NOT worse off than their parents. People who probably don't know even know what words like Class-A, ESL, Crosstalk, Resistance, and Self-Biasing means. In other words, the SAME people who made "hifi" cool in the 50's, the 70's, and '90's--the faux-audiophiles with deep pockes and empty heads who think having an awesome system you bought off-the-shelf is some sort of "badge of status". The very people who keep companies like Krell and ARC and Martin Logan in business. I don't think Krell intends to sell KAV units to "old-school" Krell devotees as main-system compnents, but maybe as "secondary systems" for bedrooms, guestrooms, etc...
In sort, the KAV line, while certainly respectable as far as audio gear goes, is sort of a symbol of what is happening in the Audiophile world today as a marketplace. Video in the new "hifi"--it is cool, trendy, and has a relatively high SAF--and therefore video/theatre systems are considered to be part of any well-equipped upper-middle-class household. Many manufacturers realize this and in a VERY slow audio market, they are jumping on the bandwagon in the hopes of salvaging slumping sales of the last decade. And much like the 'hifi" crazes of the 50s and 70s, the HomeTheater trend of the 00's will help boost sales for a lot of companies that might have otherwise died, as long as they can field reasonably-priced, slick-looking, decently-performing gear to meet the demand.
Dont get me wrong, The KAV 400 is not a bad unit, it's just not "grown up" enough to drive a speaker as notoriously difficult-to-drive as the Sequel line. I would suggest that you get a seperate amp with some juice (Krell, Sunfire, Bryston, Plinius, something like that) and use your KAV-400 as a preamp. It will excell in that capacity.
--Richard