I own a pair of B&W 801 Matrix S3. When I was buying them the dealer demoe the speakers with a Mark Levinson 332 first and then swithed to a ML 333. It was a huge diference!
As Tinman said the bass with the 333 was incredible and sepcially the control of the amplifier over the speaker was very noticable.
I have been running them with a pair of Sonic Frontiers Power 3 monos (220 tube watts). They sound magnificent but now I have the bug of going back to Solid State so I bought a pair of Threshold T400 amps. I just start using them in mono configuration (900 watts in 4 ohms) and let me tell you, the bass coming out of the 801 is deep and tight, the midrange is so transparent and effortless and highs crisp and clear. I think I am going to keep the Thresholds and sell the Sonic Frontiers.
Don't get me wrong, the SF sound beautiful. I just want to go back to SS.