When I was reading the initial question what mapman said is exactly what I was thinking. Quad 12l passive is good but not great in terms of low level listening. The Triangle Titus (especially the 202) is the absolute champ in this regard. The only issue is that the Triangle and Quad are two very different sounding speakers.
The 12l Active is much better at low level listening versus its passive sibling. This is one of the many inherant virtues of active designs and having the crossover at line level versus speaker level. (The titus has an incredibly simple speaker level crossover which is a reason it does well at low volume)
The 12l active is in a different league than both the passive and titus. The speaker can play big- where as the Titus really cant. The 12l vs 12l active is a no brainer in favor of the active IMO. However, the L2 series has a slighly different sound- especially on the top end. It is a little brighter which can actually come off as more resolving power in the listening room. I really like the L2 series.
To summarize;
Quad 12l- good speaker, smooth with an ability to play almost like a floorstander in regards to dynamics and bass.
Quad 12l active- same as above- but it does play like a floorstander. Very transparent, fast, accurate.
Quad 12l2 passive- slightly different presentation. A little hotter up top. Seems to do a tad better at low volume versus the original L series.
Titus- much different sounding versus above. ES version is larger and significantly different speaker than the XS and 202 which got the great reviews. (The Stella is more like the legacy Titus) The 202 has an incredible amount of HF energy, it takes a while to get used to but it does wonders at low volume. Midrange is very natural. Careful matching of amplification is important. Tubes, Arcam, etc. Cheap- the 202 goes in the 300s. Vinyl wrapped cabinet is no where near as nice as the Quad.