OP - Spencer is right, i don’t post much here anymore…but your thread interests me beyond the Vandersteen aspects…
ALL of the preamps so far mentioned have or are capable of significant soundstage depth… It has been a bit but i don’t remember the RP7 being deficient in that parameter… it’s no REF6 but it can’t be given $ constraints….
On fully balanced from input to output vs having balanced inputs and outputs..obviously fully balanced is more expensive to implement properly and i certainly wouldn’t use it as a filter to choose a competent high end component.
Both the Vandy amplifiers, M5 and M7 do use a balanced input…BUT…. are very inovative downstream of that and as you know designed to excell w time and phase correct powered bass Vandy speakers. I could list the ten or so circut or other details…. but you can find those on the Vandy site. I have had the M7 amplifiers w ARC Ref5se for many years. I have heard the M5 amps at length, obviously excellent w Quattro.
You might consider joining the Vandy owners forum. Richard might weigh in on extracting more image depth and “ there “ out of your setup. I have setup a few pair of Quattro….they are capable of much….
Finally…i might counsel you to wait a few months for…the Vandy preamp…rest assured the design goal is to better the REF6, which IMO is no small feat…..
I have one on order…unheard….
maybe that’s the true definition of fanboy trust :-))))