There is no reason to use a low wattage power amp when using a Rack. Unless portability is an issue. Several of my friends use rack power amps( VHT Mesa 295 and always run the power amp volume dimmed and control the output volume with your effects unit. You get a good warm sound at any volume. In the rack world preamps create all your gain not power tube distortion. I used to have el 84 amps but prefer the tone of a 6l6 or the El34.