Continuous Phase Adjustment in Subwoofers

You're right, a continuously variable phase control does just what you said. All the "Standard size" Rythmik Audio plate amps include a variable phase control, 0 to 180 degrees (which provides zero to 16 milliseconds of delay).

REL advocates their sub integration through high-level (speaker-level) connection, which feeds the subwoofer the exact signal the main speakers receive including the same amplifier voicing and timing. This natural alignment of gain and signal characteristics helps eliminate many of the integration complexities that would normally require continuous phase tweaking. 

Hope this helps! 

The non-XLR Rythmik plate amps contain both line level (on RCA jacks) and high level (on binding posts) hook up connections, as well as a continuously-variable phase control. What such a phase control offers is speaker/sub integration above and beyond what high level hookup does. In fact, the two are not at all the same thing.

The Rythmik continuously-variable phase control allows you to position the sub(s) in the best location(s) in the room in terms of the rooms modal characteristics, then the phase control (which is electronic delay of zero to 180 milliseconds, which creates zero to 16 feet of simulated physical movement) allows you to align the sub to the speaker. Rather than moving the sub(s) in relation to the speakers (for instance to move the sub, say, 2' behind the speaker), instead leave the sub in its best acoustic location and rotate the phase control to electronically create that 2' relationship between speaker and sub (two milliseconds of delay is approximately equal to 2' of physical distance).

Feeding a sub a signal that is coming from the loudspeakers amplifier may help in terms of integrating speaker and sub in areas of sonic "character", but that is not at all the same thing as sub/speaker integration in terms of the acoustic relationship between the two ("phase tweaking"). The much more common phase switch (zero OR 180 degrees, not zero TO 180 degrees)---as found on most subs, including those of REL---provides only only two speaker/sub relationships (the sub in the same polarity as the speaker, or in opposite polarity). I consider that to be of extremely limited value and use in terms of speaker/sub integration.