Glai,
I did a bit more comparison between the KXR and the REF 5SE yesterday before returning the KXR to my friend. I think both preamps are excellent but thre are some minor differences and which one is better is a personal preference.
The KXR has lower background noise and instruments are better separated and the high frequency is a bit more extended. The REF 5SE on the other hand, has vocal that is more emotionally involved. I guess that is what tubes are all about. But to my surprise, the highs and low ends are more like solid state than tubes. I was expecting soft bass and rolled off top end.
To my ears, the REF 5SE is the better preamp by a slim margin. I have always been a SS guy and this is my first tube equipment.
I look forward to Tylercoupe's comparison of these two great preamps.