9.1 Avalon OpenCores 10/100 Ethernet MAC with DM9000A

What Daixiwen meant is that DM9000A is a MAC itself, so there no point in using either TSE or Opercores MAC.

Yes, DM9000 has a MII interface, but this is only used to communicate between the two components (MAC + PHY) inside the chip. MII signals can possibly be exposed outside for connecting an external PHY.

If you want to use DM9000 you must connect it directly to your processor. I don't know if a specific DM9000 Nios II driver is available from Altera. If not, you can try using the LAN91C111 driver: you'll probably need make some changes but the two devices are similar, if I remember correctly.

Regards