If I am not mistaken, the Marantz Pearl Lite is a basically a PM8004. If correct, I can definitely assure you that this amp will be more than adequate to drive your KEF's. Then again, so would the Roksan - both would be up to task and do a very good job.
Having a Marantz PM15S2 LE, naturally I would recommend you take a longer look at the Pearl Lite, especially if you can get a used one in great condition at a good price.
Last, I don't know what your question about a 18 w tube amp has to do with the two SS integrateds that your are considering. Unless your thinking about tubes too and if you are, I wouldn't go this route with the speakers you have. The LS50's are not very efficient at 85 db and would match up better with SS. Hope some of this helps and good luck in your search.
Having a Marantz PM15S2 LE, naturally I would recommend you take a longer look at the Pearl Lite, especially if you can get a used one in great condition at a good price.
Last, I don't know what your question about a 18 w tube amp has to do with the two SS integrateds that your are considering. Unless your thinking about tubes too and if you are, I wouldn't go this route with the speakers you have. The LS50's are not very efficient at 85 db and would match up better with SS. Hope some of this helps and good luck in your search.