As I understand it:
CrossEPG, EPGRefresh & EPG-Importer are all plug-ins that allow you to fetch EPG data in various ways.
EPGRefresh and EPG-Importer are installed in OpenVIX by default, CrossEPG can be downloaded and installed from the plugins menu.
They need to be configured correctly before you can use them.
You
probably only need to use one of them.
OpenTV is an EPG transmitted by BSkyB (and maybe others that have copied the idea??) it covers all the BSkyB TV channels but, as far as I can see, no Radio channels.
One way to get the BSkyB OpenTV EPG is to configure EPGRefresh to do it.
For instance I configure EPGRefresh to tune to IEPG Data 1 (BSkyB channel 994) on 11778V for a few minutes every night (minimum 2 minutes, I use 5 minutes (300 seconds)).
You also have to make sure OpenTV is enabled in Menu / Setup / EPG / Settings.
I find it's best to set EPGRefresh to flush the EPG before refreshing.
There may be more necessary stuff I've forgotten to mention
Hope that helps.