Krell kav-400xi with show case dvd or dvd standad?

I have owned many reference class systems with both single ended and balanced. The bottom line is that both can sound wonderful, but balanced brings a heightened sense of presence, palpability, low level detail and contrast...kinda more there there!! If the system used to experience the effect isn't able to deliver the goods then so be it. I have used wilson and dynaudio speaker systems for instance, with both tube and solid state fully balanced components and cabling. The difference may be excused by some who do not give priority to the effect. Some people who listen with a distant perspective and enjoy low volume settings may not hear a difference. If you prefer being immersed in the sound field ala in the front row of the Village Vangaurd then you will require a balanced system.

isn't krell 400xi a bit overkill for B&W cm1's? the krell costs more than twice the cm1's

The Krell 400xi will remain a cornerstone in a system...speakers may change over time. However, if you don't require superior performance then look elsewhere.

That makes perfect sense. A side question though, the Krell outputs 200 wpc at 8 ohms (I think), while the CM1's are rated at 30-100 watts. Can you change the output of the Krell or how does that work?

More power is never an issue. In fact, the more power you have on hand, the less the distortion each driver will suffer. Cone control and dynamic expression will be increased as well, plus if you want to run a subwoofer or two you can use the preamp out connections on the 400xi. It is concievable that in the right room you may not need to ever change speakers.