You'll find that a small inexpensive mixer will serve you well in this regard. An AV receiver is not really equipped to deal with the signals you are trying to mix. This way you can place the EQ between the output of the mixer and an input of the receiver. However, you'll probably need some adapters to go from balanced 1/4" plugs to unbalanced RCA plugs.
The ideal solution would be to get an inexpensive 2 channel amplifier, 200W per channel, which will feature the correct input plugs.