I have owned a pair of Vandersteen subs since 2000 that I used with both the 3A's and 2CE Sigs. I just substituted the Treos in place. I ran them for about 40 hours without the subs and then turned the subs on at 82db. The Treos will do fine without the subs and that is how Doug and John Atkinson tested them, but since I already had the subs, why not use them. It certainly fills in the soundstage and impact. Part of the reason I don't have the urge to go any further up the line unless I win the Lottery. Only slight character difference I notice, is that they may be a little more forward than my other two pair, but the Sig II's may be the same. I have heard that, but have not heard a pair only know what I was told by someone who owned both series. They are however noticeably less effecient than the 2 or 3 series.