Cabasse 320 m3 Sloop Power Amp...compatibility question

Should be fine, depending on how loud you wanna go.  Won't hurt a thing if you use some common sense.  You'll get around 100db max. 

I'm driving the midbass and tweeters of my 89db sensitivity speakers with 12 watts triode (8 ohms)...no trouble in a large carpeted room, but our ideas of loud could be two different things.  

You would be a lot better off with a Dynaco ST70! 5 watts is good for headphones!

It won't hurt them no, it may not drive them to your complete satisfaction but the only way to find out is to try it.