I just bought one based on an excellent audition at my dealers, where we compared it to the big Krell Evo 402e and my PS Audio GCC-250.
The 402e was used as the reference (it really is a great sounding amp...I can't really find anything at fault with its performance). The smaller S-275 sounded very similar to the bigger 402e - which is what sold me.
The GCC-250 is truly hard to beat in the bass department, but it gives up some detail and control in the upper frequencies. The S-275 provided every bit as much bass definition, control and power as the GCC-250 and it also provided noticeably better detail and control in the presence region (better upper frequency resolution...and a bit better focus in the midrange). Frankly, I expected it to be way better than the GCC-250, but it wasn't (the little GCC-250 is that good). The S-275 does however, provide noticeably better performance in the areas where the GCC-250 is the weakest (upper frequency resolution and control). I also believe that the S-275 presented instruments in a more realistic manner (i.e.: textures, timbre, presence...etc.)
Similarly, the 402e is better in all of the above areas, but not by a very large margin. I expected the 402e to really trounce the much less expensive S-275. That wasnt the case though; the S-275 provides a very big taste of what you get with the 402e.
For what it's worth...
_Ben