your going from a good class A SS to a good tube system so there will be quite a difference in sound just with the two different amps you have listed. That's not even getting into the difference in the speakers.
Me personally I'd stick with the Harbeth speakers, and add the Lebon as its wonderful.
I have heard the Devore Gibben 8 and the orangutan o/96 along side two Harbeths p3esr's - 30.1 and a set of Dynaudio 3ways (don't recall the exact model but they were a three way design smallish tower about $5k same as the gibbon 8's) all in the same system when I was looking to replace my AudioNote ANE Lux's. I have to be honest I don't get the hoopla about the Devore speakers I found them dead sounding and a tad off in the midrange compared to the Harbeths and the dynaudios.
I actually was very surprised at how nice the Dynaudios were in comparison to the gibbon 8 it was a no contest the Dynaudios were just much better balanced imo.
I almost bought the 30.1's but ended up with Living Voice Avatar 2s (r3) in the end but they are more similar to the Harbeth sound then the others.
I have had a chance to hear the 300xs in my system and if I didn't already have a wonderful tube SET I would have bought it its really good at everything and probably better then the Line Magnetic 211 but I have not heard them both in the same system. it may come down to power here depending on what speaker you end up with.