Jwin- I wouldn't doubt what the service engineer said, a dealer told me the same thing- he told me it was due to the amount of watts the amps produce into class A after a certian amount of draw they go to a class AB operation(and believe it or not I think the smaller amps produce more class A watts then there larger counterparts, as you noted). I am VERY familar with the SC-4(non-a) and they were a very easy load on any amp we used, that being said I would say the X250 would drive the Dunlavy's with aplomb. If you are looking to invest more money I would just buy more music or perhaps look at something else to upgrade i.e. another component, but it sounds like you have good taste in gear :) so maybe that's not an issue. Happy listening!
Pass Labs X250 or X350?
I am condidering purchase of either of these two amps to drive Dunlavy SC-4as. I called Pass Labs and they indicated that the X250 was a better sounding amp than the X350 and plenty of power to drive the 91db Dunlavy speakers. They also indicated that the X600 was better sounding than the X1000. This of course was a service engineer and not a public position of the company. Any thoughts?