If you are married to making this amp sound great, I’d sell both speakers and get some high efficiency Klipsch’s, single driver Omegas, or Zu’s. I have a feeling that the Cabasse’s, while at 94 db efficient probably go well below 8 ohms. Klipsch’s sound great on low powered SE tube amps.
The 5/15 wpc Antique Sound Lab MG15siDT, if you can find one, might be a great low powered choice with the Cabasse’s or a PP EL84 amp that would give you approx 15-20 wpc.