Hi Guys
The POD XT works very well in a full range system such as headphones, active full range speakers/studio monitors, hi-fi speakers, PA speakers, Keyboard amps. Of course the final result still depends on the performance of these full range speakers. For example, if you plug them into small computer speakers, they will sound small as compared to stage loudspeakers.
Leb is absolutely right about these speakers having a flat EQ response. The POD XT have to be setup in "Direct" mode under "What are you connecting to?" menu page. The output from the POD XT would be as if the amp model chosen is being MIC-ed up and going straight into the full range system.
Of course the POD XT works perfectly fine when connected to a guitar amp too which have a mid frequency response. In this case you need to select "Combo" or "Stack" under the "What are you connecting to?" page. This will make the guitar amp being connected sound like the other amps modeled into the POD XT.
Cheers!