What Sensitivity with Tube Components?

Nothing between speaker, yes one side has heavy curtains which I have closed. Other side does not.

briefly looked at the manual. So you are using pure direct mode, cd direct amp ?When I said the 4ohm setting earlier I was implying for the tube amp. but this is an interesting amp.  

I have not tried this setting in the "Low" (4 ohm) setting but maybe it would be worth a try?

I am not familiar with that amp but would say - Yes.
See the wording here.  

http://hometheaterhifi.com/reviews/receiver-processor/receivers/yamaha-r-s700-stereo-receiver/

the R-S700 is bi-wire ready. In this case, it uses both sets of internal amplifiers (Speakers A & B) for one pair of bi-wired speakers. This implies a true bi-wired scenario, where separate discrete amplifiers are used for the tweeter/mid-range and woofer section of your bi-wire-able speakers.
Note that if you do use this bi-wiring feature, it is important to select the proper impedance (high or low) setting for the receiver. The high setting allows bi-wiring speakers with 6 Ohm impedance or higher, while the low setting allows bi-wiring of speakers rated 4 Ohms and higher. Similarly, the high/low impedance switch needs to be properly set for standard wiring too.

As far as wattage - B&W benefit from more good wattage.   I would try the above settings first and see how you like it. I believe you will get more oomph - and it will be a warmer sound.    

Do I consider Class A, B, AB Tube amplification?

That can become a long discussion.  there are real amp experts here that can help you out more.
Push Pull a/b tube amp works well from my own experience with lower efficiency bass needs.  And yes stands would improve things alot - but thats a no due to your wife saying so.    

Indeed!
Thanks for the input.

Since you're not using stands, are you using some kind of acoustic footer so that the speaker is decoupled from the furniture? IOW, are the bottom of your speakers sitting on the bookcase or are they raised?

If brightness is your problem it is the B&W speakers. With the free-mounted  aluminum tweeter you can change your gear till the cows come home and they will always be bright. My friend had the 805’s and they would drive you right  out of the room! BTW, I had the original 802's many moons ago and they were also bright! Power is not the problem,the speakers are!