Now you can get a stereo receiver with a phono input for $100 but it doesn't have a line level sub output.
If your subwoofer has speaker level inputs you could connect the bookshelf speakers to Speaker A outputs and the sub to Speaker B.
If your subwoofer has speaker level inputs AND outputs you could wire the receiver to the sub with speaker A outputs and then the bookshelf speakers directly to the subwoofer. You would then use the subwoofer crossover dial to set your crossover point.
What subwoofer do you have?