ah ok, it sounds like if building a new seq, these should be on the main panel, and only users with existing v2 seq would want to put them on the extension. just to be clear why i asked this: i am planning to build an extension module and connect it to the main seq with say a db9 connector, carrying only the din/dout signals. sounds like if other folks follow this and want the track group buttons on the extension (i think only makes sense for existing v2 seq), they will need to add these... i suspected this was too expensive, sounds like the 20ms would be fine though. when pressing several buttons at once, the lag would be <number of simultaneous buttons> * 20mS, right? thanks for the infos!