Get a couple rca y adapters (2fmale to 1 male) and some cheap rca connectors from radio shack. Make yourself a few load plug ins by soldering resistors onto the connectors and the y adapter will put them in parallel with the input. This is a cheap fast way to sample different loading. Use good resistors. If you find something you like you can fashion something more permanent or just use the jig. There's no hard and fast rule its different with every cart, pre, system, combo.