I inherited a Marantz NR1200 Receiver, which has a HEOS function and although I am intelligent enough to operate the 2.1 Receiver connected to my Turntable, DAT Recorder, Compact Cassette Recorder, CD Changer, and Airplay devices, I do not understand what HEOS is, or what it does. Here's why, the Marantz does not come with a manual so downloading one is necessary and it's over 200 pages. So far, I have not been interested in the HEOS feature enough to do that downloading or reading of manual to get a sense of HEOS. I suspect that others, many others, are about as lazy as me, or having purchased Marantz or Denon electronics for a specific traditional role do not have an interest in the HEOS feature. I'm going to stick around here to see what I can learn about HEOS.