I know this has been asked a few times, though search came up empty. With a move recently thought I run a quick test to see if I could replace the Quad 12L actives with the more simple to use Audioengine A5s. Was kinda disappointed when the 12Ls arrived that they required a pre or variable output. Was hoping the level switches would be good enough. And since I installed, the girlfriend has shown little interest hunting down even more switches behind boxes to activate.
Anyway, placed the A5s on top of the 12Ls which are on speaker stands about 5 feet apart. Sat nearly the same back. Threw on Bill Frisell's Blues Dream on the DVD-2900 plugged into the Parasound 1600 and then the GS-1 (A5 loop/12L pre) and alternated.
As it was a personal test about replacement, that was answered quickly after a single CD (and thus maybe not much use to others), I won't be going into lots of details, but I'll be sticking with the 12Ls for primary use for now. The A5s will return to the bedroom, but if the above real practical considerations (toss size and ipod/airport connections in there also) increase, who knows?
Both sounded damn good for their likely uses, and with their prices so different are arguably not in the same class, but I've got both here and can say the 12Ls beat the A5s in every basic sonic test - subtlety in quiet passages, staging, separation, detail, clarity, bottom slam, balance, decay, etc. A5s most obviously sounded a bit congested and Grado-like forced in comparison. Others have said the A5s may be held back by their amp, which while I never felt before, is a possibility.
Most of this was apparent by the first tune, but again this is only in comparison. I could easily live with either set and I think the A5s are killer at their price (especially with web coupons floating around). Hard to comment on bang-for-buck or upgrade-worth as these are near-field monitors and setups using them tend to be compromised in one way or another. If three feet apart on a desk and two feet from your head their differences would likely lessen.
I know a few other members have/had both sets and can perhaps chime in also.