Nios SOPC not in toplevel

I created an SOPC with an Nios and a tse_mac. If I instantiate it directly in the fpga toplevel, its working with the simple_socket_server example. Now I wanted to instantiate it one hierarchy level deeper, just to put in all the stuff (pll, reset generation, pio etc.) that only the SOPC needs and to have only the connections to the rest of my design that i need for further data processing. But somehow, the SOPC is not working in the sub-level. To minimize the possible errors, now I tried to build a very simple module around the SOPC without any additional logic, I just wired the in- and output ports. I left the PLL and reset generation outside at the toplevel, but still the socket server is not working. If I start the Nios software, it finds the Ethernet MAC and PHY and tells me that it has opened the sockets, but I cannot connect to it.