[Ron Ramirez]

I think the best way to go would be to make new line outputs just before the standalone's volume controls, and then disconnect B+ from the preamp and output amp transistors, in effect killing the amplifier section. Otherwise you would need to have a load across your speaker terminals all the time, a waste of power. You would end up with a tape deck without the amplifier, which I believe is your goal. As Arran noted, however, you'll need a schematic.