I'm considering buying the CD6004, but wondered if I could use it as a stand-alone item? As I don't have room for speakers I will be using headphones, so is it necessary to buy the matching amp as well? I've been using an old (1980's) Technics SL-PJ26A CDP and a more recent Sony CMT-SPZ90DB, but can't hear much difference between them. Would I really find a big difference with the Marantz?