Tracks you download from here will be BTB tracks which are only compatible with RSRBR.
If you're not using RSRBR, I can't really help (and not many others can, since it's the plugin of choice around here).
I'm not at my PC atm, so I can't check the details, but off the top of my head, downloaded tracks don't go in the RXContent folder, they need to be placed in RXRSRBR or something like that. You can then launch the tracks via RSCenter rather than messing around in the plugin menus.
I've played around with BTB and RSRBR and I seem to remember RXContent gets cleared down pretty regularly - as if it's just a temporary store used by the plugin.