to my knowledge there are some that prefer one over the other, with the UP-4 being most often characterized as "lively," and the DP-6 as "refined." of course one's own results would depend on system context and synergy. there is also a significant price differential if budget is a concern. personally, i am the happy owner of a DP-6, and would say it lacks nothing in the "liveliness" department.
perhaps sorasound (the audiogon dealer) could give you some input and perspective. he (mehran) answers emails promptly and is a friendly, communicative, and intelligent fellow.
