I would not say that the Krell is "better" than the Marantz. They are different. The Marantz is priced lower because of economy of scale. It has a huge retail network and will be able to sell significantly more units than the Krell Foundation because of this huge network, hence a lower price that is more accessible to people.
The Marantz is an excellent unit with excellent design. It has a huge power supply for an HT Processor (40,000uf if I remember right, I think it was 4 x 10,000uf capacitors). It also has a significant amount of power supply capacitors directly on the analog circuits. That being said, it is voiced to be on the warm side (like a McIntosh in a way).
The Krell, on the other hand, is very fast, high resolution, lots of fast attack. This is great if you want a lot of excitement during movies (action scenes, etc.). I will say that the Krell power supply is sized decent, but not great. This means that the Krell is not going to be as full in the sound as the Marantz (bass / midbass / midrange).
At this point, it becomes a matter of matching equipment. If you were going after a warm/full Integrated Amp like the McIntosh MA8000, then the Krell would be a very good match to provide a little more kick for HT purposes. The warm/full McIntosh would round out the leanness of the Krell sound. The Krell would not match well with a very fast/detailed amp. The sound would just be too lean/thin/bright in the end.
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Another note. These are HT Processors we are talking about, which means they do not have built in amplifiers. You will have to get an external amplifier to power the center/surround speakers. This is, ultimately, the better way to go in my opinion because you are not going to get the quality of sound from a AV receiver (AVR) that you are from a good processor and amplifier combination. This will also allow you to choose an amplifier that is very similar to the 2-channel integrated. I believe this is very important because matching the "voice" of the front 3 speakers is most critical in HT. If the amp is very different for center channel, you will definitely hear a change in sound when sounds pan from left to right (which happens a lot in movies). Some companies will have a 3 or 5 channel amplifier available.