The CS 4398 has a kind of analogue quality. It offers a more relaxed, warmer sound. It gives a large soundstage by bringing out more of the mid. The top end is softer and less extended. The bass is less defined. It is very forgiving with recordings of lesser quality and it seems well adapted to shrill sounding recordings of pop music. It seems a bit compressed and it does not excel at pin point reproduction of the room ambiance, nor does it reveal the more hidden information like breathing noises etc.
The BB PCM 1793 is a more technical affair. On first hearing it is much more clinical with less midband warmth. However, it does give much more ambiance information, and it retains the original dynamics far better. Weak sounds like breathing is much more audible. The bass is much tighter and less compressed. The top end is more extended and less smeared. When listening to high quality acoustical recordings (classical or jazz), it is a treat, but when fed with low-fi pop music it is much less forgiving.