I don't know the Marantz, but according to reviews such as the one in TAS it has an uncommonly good phono stage for an integrated amp. Taking that as fact, I would suggest you hold on to the money you've now got and save up some more.
While I've no doubt that either phono stage will better the built-in one, I very much doubt that either will make sit back and think "WOW".
While I've no doubt that either phono stage will better the built-in one, I very much doubt that either will make sit back and think "WOW".