What Sensitivity with Tube Components?

All makes sense but you are saying that these speakers should be connected to a 4 ohm output? The Yamaha R-S700 has an impedance switch on the rear which allows for 4-8 ohm speaker set ups, bi-wire & not. (see page 13 manual)
I have not tried this setting in the "Low" (4 ohm) setting but maybe it would be worth a try?
Also, These speaker are at least 1.5 fee from the rear wall but I've always felt speaker stands would help. (The wife is not into this as much as I am) So on the built in book case the remain!
As for tube, you suggest as many watts as I could afford. You can buy a Jolida 100 watt Tube for under $2,500.00. So price does not always seem to dictate great sound.
Do I consider Class A, B, AB Tube amplification?
Thanks.

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?