For a speaker with as low sensitivity as the Devore Super 9, you might want to look at the Art Audio Elise. It is 16w (double that of the Luxman or Air Tight) and uses a 520B which is a 300B derivative from Emission Labs and very similar to the old KR VV 52B.
It is a wonderful sounding amp with lush mids and better bass than you could expect from a SET. This unit replaced the Jota in the Art Audio lineup and is the amp in my profile photo.
A 520B based unit will be much closer to the sound profile of a 300B than an 845 or 211 will be. The other option would be to look at a 300B parallel SET like the Art Audio Argento but then you are running four 300Bs which can be brutally expensive to maintain longer term.
I am sure there are other 520B based units or other 300B parallel SETs which may solve your issue. I just don't know them off hand.
Full disclosure, I am the importer for Art Audio. I am pointing these units out because they solve the marginal challenge you are facing in terms of power. We have plenty of 3rd party review of our amps at a variety of sites.
Good luck!