What Sensitivity with Tube Components?

Thanks for the replies,
B&W CM6s speakers (for now)
Speakers situated on solid bookcase/cabinet about 7 feet apart right to left. Listening position about 7 feet from speaker position. I listen loud enough to hear it! (no distortion!!)
Room is about 24x24 feet with banks of windows on two sides.

Listen to a lot of Blues/Adult Rock, some Jazz and some Classical.

Look forward to any suggestions.

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

About 6 inches from rear wall both speaker have clear field horizontally. Windows are about 3-5 feet from speakers.
Current Amp/Receiver is Yamaha R-S700.
Yes, speakers like those.
I have decent cables but system sound "bright" to me. Granted, there is room for improvement all the way around. Looking for more "warmth."
You can see, this is a "budget" system compared to many. I'm open to suggestions.

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.

Indeed!
Thanks for the input.

Yes, the speakers are on the rubber feet supplied with speakers. I was afraid that the answer lay in the speakers themselves. It is unfortunate that today you can spend $2,000.00 on speakers and not be satisfied. Sure, in the total these are inexpensive speakers and maybe I expect too much?
I go back to 12 inch woofers in my old AR3a's. Apples to oranges I know.

ct0517, yes when I did switch the impedance and switch there was a definitive change, and not for the better. Mid-range was more pronounced but almost to the point of distortion. (only way I can describe it) Otherwise I didn't notice much too much change. I didn't leave it there for too long as I was not happy with the change.
Currently I am using 12 ga cables with bi-wire at the speaker end only. Perhaps I will try a true bi-wire set up with the switch set to low. Worth a try.
I listened to these speakers at my local Mcintosh dealer, B&Ws & Mcintosh 275 amp. I was very disappointed with the sound, actually the Yamaha was more to my liking. So to say that B&W speakers may not be "Tube Friendly" sounds quite plausible.

Mother's milk! I love it! ;-)
All very good info. I'm glad I posted this question on this forum.
I have another set of 12 ga cables so I will give the bi-wire a try. As said, it cost's nothing! I'll let you all know how it works out.

Thank you all!

Yup, that is the message I'm getting. Makes total sense and I'm glad I posted before I took the plunge into tube amplification. I've had these B&W speakers for about 1 year and I always intended to "upgrade" at some point. This discussion has shown me that upgrading my speakers with a view toward going over to tube amplification requires serious homework before making that switch. It also shows me that where I buy is as important as what I buy. If the guy selling me the gear has no clue about what he is selling then chances are I will end up not being happy.
Mcintosh MC275 MK6 - B&W CM6 S2 don't match up very well as proved to me first hand.

An update; I did try the Bi-Wire set up with my speakers & Amp. With the Impedance switch set to Low and using two sets of 12 GA cables there was a bit more "oomph" but also seemed to be a bit of distortion again in mid-range. Switching back to impedance setting High cleaned up the distortion and sounded more like the cables single end at the amp and Bi-Wire at the speakers. I was using two different brand of cables so that must be taken into consideration but I could not justify using 2 cables as there was not a great deal of improvement. Speaker placement is highly important and I guess right now I'm going to have to be satisfied with what I have. Which is not all that bad considering.
Thanks to all for the help!

Good point.