Jadis JA30 Mk2, how great???

@samhvcc Congratulations on becoming a new JA30Mk2 owner.
The amps do need a little run in before they can show their full potential, like all new gear. I would also suggest, like the manual states that you don’t listen that carefully until about 1.5 hours of playing time has gone by. The large transformers definitely do need some time to get ’warmed’ up. Nonetheless, the amps sound amazing from turn on...just a little better after the transformers get ’warmed’. Also, after you have lived with your amps for a while, I would highly recommend rolling in some NOS tubes into the 12Ax7 and 12Au7 positions. I just rolled in some NOS Telefunken 12Au7 smooth plates and some NOS Siemens 12AX7’s - this makes for a big upswing in SQ.
As to your question about a 300B amp, I am not understanding your point. The Jadis can deliver up to 45watts/ch...where does 10watt/ch come from?

The SE300B is a different Jadis amp actually and it looks to be parallel single ended and not pushpull hence the lower wattage.
http://www.jadis-electronics.com/en/se300b-43.php

Got it. I'm not really a fan of 300B single ended amps. Not because I don't think they sound good, but more because they are so very limiting as to the speakers that you can match them to. Plus, I think in many cases the 300B tube is more susceptible to noise from microphonics. 
In that perspective, I much prefer an 845 ( which Jadis also makes).

Jadis is  one of those companies that just consistently has  the knack of  building beautiful sounding emotionally engaging amplifiers that connect the listener to the music. There's obviously something they understand  and are executing  right.  

I'm a 300b SET aficianodo through and through. I haven't the opportunity to hear the Jadis SET offerings but I'm confident that they got it right. I heard a Jadis el34 push pull integrated (Not even one of their higher level models)  and it was very good sounding.  It displayed that special ability to pull you deep into the music..

It they can achieve this level of sound quality with an el34, I can imagine what they're capable of with a 300b in their  upper level range of mono block amplifiers.  As daveyf noted you just need the appropriate speaker matchfor the amplifier. 
Jadis is exceptionally adept at reproducing music beautifully. 
Charles 

Indeed, Jadis does make beautiful sounding and emotionally engaging amplifiers. To that, I think their build quality is basically second to none.
IMO, if one is looking for a tube based amp, then these need to be on anyone's short list.