I’d suggest going with the Treo and 1-4 moderately sized subs would definitely be the more versatile option when compared to a pair of Quatros with no subs. I’ve never compared the Treos to the Quatros by themselves but I’m still fairly certain that either’s overall performance would be improved with even just a pair of well positioned subs. I maintain this opinion even though I’m aware the Quatros have built in powered subs and claimed bass extension down to 24 Hz +/- 2 dB.
The main issue, from my perspective, is that these are both floor standing tower speakers and that virtually every owner is going to position them in their rooms so that the optimum midrange/treble response and stereo imaging is attained at the designated listening seat.
The bass drivers are just along for the ride, located in the room a matter of inches or feet directly below the midrange and treble drivers. The apparent assumption that this positioning will also provide optimal bass performance at the listening seat is highly unlikely bordering on fat chance and no way. I believe it’s a distinct and very significant advantage to have independently positioned bass producing drivers in virtually any room and any system.
I even suspect that a pair of Treos, combined with a $2,800 Audio Kinesis Swarm 4-sub distributed bass array(dba) system, would outperform a pair of Quatros without additional sub assistance. It’s also very possible a pair of Treos, combined with just a pair of good quality and well positioned subs (a used pair of Vandersteen 2wq subs for example), could outperform a pair of Quatros without additional sub assistance when judged from the designated listening seat.
I should mention I highly respect the Quatros along with Vandersteen speakers in general and my intention is not to disparage them. It’s just that I know, through research and personal experience, the near sota bass response attainable with at least two and up to four good quality, well positioned and properly configured subs in virtually any room and system. I think a pair of Treos combined with a Swarm type bass system, at a combined price new of about $9,800, would be an excellent performer and a unique audio bargain.
Best wishes,
Tim