The X250 is a more recent design/build and has received its share of rave reviews. The X350 has reached a pinnacle of its own in the TAS recommended components listing. I think you have reached the point of diminishing returns in attempts to gather information. You are at the point where listening is the only thing that may provide you with the answers you are looking for. At least, this is the point at which I start pounding turf.
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?