Just to be clear, I'm sure the Aleph 3 is a superb amp - I have heard nothing but positive remarks and reviews of Pass amps, and would love to try one in my system some day. I've never heard one under any circumstances, so I can't personally give it the thumbs up or down.
Also, absolutely if you're willing to live with the heat and the energy bills, go pure class A. I wouldn't try to dissuade anyone from going pure class A for performance - in fact, just the opposite. I believe the KSA50s is pure class A - the KAV-250a is absolutely NOT, and I didn't mean to imply that it was.
Kyongjin - the KAV250 and the 300i are VERY different beasts. The 300i has 150w/ch (the new iL has 200) and the KAV250 has 250w/ch. But, much more than the raw power, the KAV250 is at least a whole notch up in performance, retailing for more than the 300i did (does) as just an amp. Moreover, the reviews of the 300i, both professional and consumer, have recounted spotty performance, whereas the reviews of the KAV250 have been largely overwhelmingly positive. One of the Robert's for TAS (Hartley or Greene, I can never keep them straight), reviewed the 250 and gave it very high praise. It's currently in the perfect sweet spot of purchasing used - you can find show-room new condition used units (or dealer close-outs) that are only 1-2 years old, since Krell just announced new models, and it's available right at, or about, your budget price.
Although I have no problem recommending this as at least an option to think about (and encouraging you to not use your 300i experience as a reference), you may well prefer the sound of another amp, and I certainly wouldn't attempt to tell you you shouldn't. The KSA50s can certainly be had used for less than $1500 (probably closer to $1000). The Pass amps are very highly regarded and may be the best choice for your tastes. -Kirk