I have not done this in awhile, but I pulled up Task Manager the other day out of curiousity. I was playing a 5.1 SACD-DSF file with on the fly conversion to 176k PCM plus bass management plus Dirac Live EQ via the VST plugin. Total CPU usage was in about the 8-15% range. RAM usage was fairly constant at about 4 GB.
My PC is about a 4 year old I7 with 16 GB RAM. Files are served from a NAS. I do not use memory play. There is a GPU, via which I was displaying these results as they occurred.
I am on the latest JR 23 - 32 bit, using Win 7 Pro 64 bit. My Webroot AV/Firewall is always on by choice.
I have never seen any evidence of JRiver using excessive resources.