I speak on this subject with a fair amount of experience, though I was not involved with the brand as a product manager until a bit later on. I've spent a fair amount of time looking at response graphs & other documentation as a result.
I will say this again, hopefully with more clarity this time: if you try and drive any ADS bookshelf speaker into the output levels the 1290/1590/1230/1530 can manage, you will just make it mad and/or break it. It is physically impossible to achieve that level of performance with so little displacement.
These later. smaller bookshelf models were intended for use with subwoofers (in larger rooms or when played at high output levels) or for use in near-field situations where the extended frequency response and modest efficiency can be best utilized. In a larger room or when higher output levels are required, either go big or biamp with a sub.
I also think the later systems are touchier about their power bandwidth. They are lower in efficiency (partly because the cabinet air volumes shrank over time) and the drivers can be fragile. Push them too hard trying to achieve higher output levels and they get strident, then break. Again, that's because by this time a/d/s/ was designing around 2.1 systems using bookshelf speakers and powered and passive subwoofers. Those smaller models are absolutely fabulous when you biamp them with a sub, but nowhere near as pleasant to listen to if you're running them full range with any real power behind them.
Keep in mind when the L420/L520 were designed, ADS had not made their evolutionary step into satellite/subwoofer system design so the tuning of those small speakers was intended to allow them to be effective when running fullrange. Not as much the case by the time the SAT series came along (SAT? Hello? I think that name should tell us something!). So, they may sound better to you than the SAT6 or SAT7 when used as stand-alone pairs but again the later ones were designed for being biamped with a subwoofer.
That's why I said this comparison was apples and oranges.
As to me being blinded by my own collection, quite the opposite. I bought these models because I know how spectacular they can sound when utilized properly. That means I DO have a C10ps powered sub to go with the L400's in my office at work, and an HT12ps sub in my HT system with the HT800 proto towers, but the L1230 and L1290/2 are on their own in my big 2 channel system. They don't need a sub to be effective.
I just think you're being unrealistic in comparing such drastically different speakers. I assure you a pair of the SAT speakers can do anything you need them to, if you set them up correctly in a 2.1 system.
John
P.S. What you are characterizing as a "complete lack of midrange" is in fact a superbly flat response curve. There was nothing wrong with the acoustics of these speakers.
