Hi Carlo - Yes, certainly the push/pull Cary should be fine and likely would posess many similar qualities of the Mono 10's I liked so much. I can't truly give you an authorative opinion on either having not actually heard them, only read the various posts and reviews referring to them. I've owned a couple of Cary Preamps, which I've liked very much, and a good friend owns a modified SLM-70 which he uses to push his Quad 988's. I think they make fine products and their customer service, and overall reputation is excellent. I would definitely consider either amp you mentioned, perhaps leaning a bit towards the 2A3 PP design. The price on the 300sei does not seem out of line given the blue book, though you may be able to get a better deal with some patience, and make a lower offer on this one. There are certainly other options out there as well, but Cary does represent a solid investment in my mind.
Marco