@MatthiasBTH Certainly.  You just need to buy a second EAP.  Connect it to your router (directly or using a switch).  Set both AP's to the same SSID(s) (different channels).  Clients will lease their IP's from your router an will all be on the same subnet.

You can do this using the built in web management for each EAP.  But, you can leverage the OC200 for centralized management (or use the free software from TP-Link) which is much nicer.  

I have two EAP225V3's for my home network with the OC200.  One AP is directly connected to my Fios Router vua Ethernet (as is the OC200).  The other is connected via Ethernet using a MOCA (coax) bridge.