We used to carry both JM Reynaud and Reference 3A, and we sell a lot of SET amps. We are very deliberate about which speakers we sell with SET so I'll jump in here...
JM Reynaud does not make any speakers that I have heard which run well on SET at all. Most of them need pretty big push pull - at least 50 wpc. for optimal performance. We had a pair of Twins and Trentes in here recently and even on 30 wpc. push pull they were closed down, had poor bass control, and it was clear that they needed more power. We spent a while trying to analyse the problem and couldn't come up with anything conclusive. The impedance of the JM Reynauds is fairly benign - but I think there is something capacitant in the crossover, and the woofer is definitely putting out a lot of back EMF. The result is that when the bass kicks in on the JM Reynaud's you end up with closed down mids and shrill highs. Forget SET with anything from JM Reynaud period. We found that they sounded quite nice on 70 wpc. push pull monoblocks, so I say 50 wpc. minimum and consider going closer to 100 wpc. if you wish to run JMR on tubes.
The de Capo's are a different story. They are what I call semi-SET friendly and definitely push pull friendly. Depending on your room size, listening levels, etc. you can sometimes get away with SET on the de Capo's. They are marketed as being extremely tube friendly and the marketing is somewhat exaggerated and embellished. Their impedance is fairly high and flat, and the sensitivity is reasonably high. But they have no crossover on the woofer so they put out Back EMF like crazy when you start thumping away on the woofer. This means that if you listen loud or are in a large room and must turn up the amp to fill the room with sound, you will start to run out of power very quickly as the amplifier sees lowering impedance as a result of Back EMF. For moderate listening levels in medium sized rooms you can get away with 300B's on de Capo's, and the combination will sound lovely as the de Capo's _do_ sound their best on tubes. I would never run them on any less power however, and if you listen a louder levels or have a bigger room (or listen to material with a lot of deep bass) you will want bigger SET (i.e. parallel or 845's, etc.) or quite possibly push pull.
Please understand that I am not dumping on either speaker - they are both fine examples of loudspeaker design and can be highly enjoyable if mated with the proper amp. I am simply offering our experiences with a variety of SET and push pull amps on these two speaker lines in the hopes that it will enable you to get the best sound should you choose either. We are very rigorous with speakers when we evaluate them on SET amps because we want to make sure customers are getting the most out of their investment.