Thanks for your interest! EPx is still in the early stages. So far most of the effort has been focused on getting the development effort off the ground. We do not have an end-user installation available for testing yet. When we do have an installation ready, you can be sure we will announce it here.
EPx is strictly a simulation engine (same as EnergyPlus). Simergy is a graphical user interface that uses EnergyPlus as the simulation engine. Simergy could optionally use the EPx engine, but I don't see any obvious reasons for combining the efforts...they are two different things.
OpenStudio vs. Simergy is a bit off-topic for this group. You might want to raise that question on the EnergyPlus Yahoo! group.