I have a tube amp with only one output jack (rated for 8 Ohms). I usually use an 8 Ohm cabinet when performing, but occasionally would like to use a second 8 Ohm cabinet or use a cabinet with a different (lower) impedance. Are there any devices available the can be plugged in-between the amp/cabinets to solve this problem? Maybe a power attenuator? I'm thinking it may be best to just replace the output transformer with one that has an 8 Ohm and 4 Ohm tap and reconfigure the line-out jack to a second cabinet jack.