Cary 300 integrated, Devore speakers

With my 30W class A amp and the benign load of the Super 8's, it feels like I have a lot of reserve power. Your amp is Class A, probably with high current, you really need to find the recommended minimum power.
I've heard it's tough to reach John Devore, but I suggest you try. Also use Google, I'll research it as well.

Does your amp have 16ohm taps or 4, 8ohm?
 

It's possible that he rates his speakers conservatively, but the real advantage to Devore's speakers is the high and relatively flat impedance curve. In independent testing I've never seen his tower speakers perform higher than the rated sensitivity.

I own the Super 8's, love them, and I know my next speakers will be Devores.

Super 8's and his other Gibbons have about 90.5 - 92dB sens. All have a nominal impedance of 8 ohms and are easy to drive. The Orangutans have a high sensitivity rating and can be used with low-power amps.
I use a 30W Atma-sphere amp and it mates so well with Super 8's. Excellent control of the bass and plenty of power throughout dynamic peaks.

I don't know how your 15W amp would perform, plus you're using 300b power tubes. Does Devore list minimum power needed in the specs?