How many watts per channel are enough?

Ditto on most of the thoughts here.

34 watts is not enough headroom for the 89 db efficient speakers you have. On the other hand, 34 watts would be plenty for my 101 db efficient Zu Superflys.

Go for at least 50 wpc, preferably 75 or 100 wpc.

As others have eluded to, not all watts are the same. In particular tube amps are'nt the same as SS, also SET amp watts are'nt the same as a push pull tube amp. The most suprising is SET amps. You really can drive speakers you should'nt be able to. This may be due to the high current and large output transformers. There is also the issue of driving into clipping, tube distortion seems much more acceptable, than SS distortion.

My 20watt Ayon Spark, sounds significantly louder and more dynamic, than the 50watt Class A Pathos Inpol2, I also use.

All I am saying is, what should'nt work on paper, often seems to and vice versa. The only answer, as always, is to try the amp with your speakers, in your room.

"Zd542, legally they would all be required to put out at least 100 Watts. I agree that 89 dB isn't that inefficient, but 39 Watts is really on the low side for a room of that size."

I didn't check the UCC before I posted so I'll take your word for the legal aspect of it. Is far as my post, I'm 100% correct. There's no standard for ratings. The question is not if 34 watts are enough but how good those watts are. I'm not guessing on this. You don't have to take my word for it. If you don't believe me look into it.

Hey, follow K.I.S.S. (keep it simple, stupid), the general rule of thumb is to use double the required RMS output, fuse or breaker protect the speakers, and listen for audible distortion. This setup can even be used to lower THD. If you have 8 Ohm speakers and a 4 Ohm amp you can cut THD in half while maintaining proper power output. I, for instance, use 12 ohm speakers L/C/R/SR/SL on a 8 ohm amp. This technique works wonders for sound quality while maintaining volume levels.

Zd 452, I agree with you. When I bought my speakers last year the guy was running a 40 watt tube amp on them. I could not believe 40 watts would power these speakers. They are a difficult load at 85db sensitivity. When I got them home my 100 watt tube amp almost ran out of steam at high levels. All watts are not created the same.