I am having a lot of problems with JRiver and HEOS, too. This seems to be an issue worth resolving considering how many people use Denon or Marantz receivers. I had issues with a new Denon AVR-X4400H that I ended up returning and now have the same issues, but worse, with a new Marantz SR7013.
I have music stored on a Synology NAS. I have JRiver on a Windows 7 machine in 64 bit. I use JRemote on an iPad to play music on the stereo. I had no problems with my old Onkyo. With the Denon and Marantz, I can no longer fast-forward. With the Marantz, in particular, there is a significant lag between tapping a control button on my PC or in JRemote and getting a response from the stereo. For example, if I hit next song, nothing happens for about 3 seconds, then the next song begins to play maybe a few seconds later. So, it is not exactly "snappy." Often, it hangs entirely, and I cannot stop music playback on my PC or in JRemote. I have shut down the programs. Even then, the Marantz sometimes will turn on by itself and begin playing again! If I manage to pause a song, it goes back to the beginning when I hit the play button to resume.
I downloaded WhiteBear DMR Analyzer and will post test results in a separate response. The only changes I made per the analyzer were to uncheck "DLNA" and "DLNA Extras" under Add or Configure DLNA Servers / Advanced. This change made no difference in performance.