Speaker power rating and amplification???

Check the efficiency rating on the B&W DM604s. If the rating is 87db or higher, either amplifier should drive the speakers efficiently without qualification. The A150 would probably provide a tighter grip with transients that demand higher power. Played at reasonable volumes, the A80 will drive the speakers effectively, but will not be quite as efficient. However, in many amplifier lines that I have auditioned, I find the more reasonably powered amps to be a tad sweeter sounding. I purchased a Threshold T-200 way back when, and preferred the musicality of this amp over the T-400, so I own 100 Class A watts per channel at 8 ohms. This amp puts out close to 200 watts per channel at 4 ohms.
I believe that your B&W speakers are rated 8 ohms. If they were 4 ohm speakers, they might be more difficult to drive and then the A150 would be the clear winner.

that shouldnt be too much power for your s2's. more importantly find out the speakers efficency rating. the lower the number, the harder the speaker is to drive, or in other words, the more power you need. anything over 90db (sensitivity is rated in decibels) is considered high efficiency. lastly, what impedence are the speakers...Ohms...usually you'll see an amp rated at 100w at 8 ohms, and 200w at 4. 4 ohms are harder to drive, and therefor need the additional power. im sure youl get a lot of answers, with much more detail and specifics..

Too much power isn't really ever going to be a problem. Too little power used injudiciously may be. That's the rule of thumb that I learned many years ago, and I still think that it makes good sense. I've run many a setup with amps powered way above the "suggested" speaker rating with no problem whatsoever. Unless you turn the thing up to 11, fret not.

Thanks for the responses. The speakers in question are rated at: 90db, which I am assuming from the above comments means that either amp will do a good job driving the speakers? I plan on attempting to utilize both before making a decision on which to use. Strange finding, the owners manual states Power handling: 25-200W continuous into 8ohm while the back of the speaker shows 150W max. amp power?

Low powered amplifiers driven to clipping are more likely to damage a speaker than too much power. Distortion is what takes out most drivers unless there is a severe mismatch in terms of power sent to the speaker. In your case, either will work just fine.