The Rhythm 1.1 inverts phase, which means that you should reverse the positive and negative leads of your speaker cable at one end (at the speaker only, for example) in order to present music in phase. If you have another phase-inverting component in your system, no reversing of leads is necessary.
Why do we invert phase?
The natural result of a single stage of amplification is that the phase of your music gets inverted. In order to “switch it back” to correct phase, we would have to run your music through a second stage of amplification, such as another pair of tubes. Or, we would have to employ some other phase inverting device in the signal path. From a sonic purity standpoint, we believe these measures are undesirable.