Those are two very different speakers you are asking about. I have owned Kestrels for about six years now and have tried numerous times to upgrade from them. One of those attempts was with a pair of Proac Response 1.5s. The Proacs were excellent speakers with good bottom end and plenty of detail. What they lacked was the musicality of the Kestrels.
If you look at my system page you will see the various speakers I have tried to replace the Kestrels with. In a small room, with modest electronincs, it is very hard to beat the Kestrels. They sound more like music, not a stereo playing, but music to me than any other speaker I have owned.
Although I only briefly used them with tubes, I can't say how they would work with your amp. My understanding is they are good with tubes. I can say they maintain their tonal balance at low volumes very well.
The problem is finding a pair. And if you do find a pair, what condition they are in as they are going to be ten years old. They use time aligned drivers and simple 1st order crossovers with very high quality parts so if they were treated well they should last a while. Good luck whichever way you go.c
