ATC active vs. passive

@ei001h 1. is it possible to self modify Active into passive down the line if get tired of active and would like to try other amps ?  Is it possible to purchase passive crossover and swap them at home? 

NO this is not possible due to the calibration necessary to set individual driver loves to build cohesive anaphase linear system.  Theoretically you could purchase an ATC passive crossover (for the model you have). Installing it would not be something to do at home.  You'd have to remove most of the drivers to get inside the box. 

2. 150 is considerably wider baffle than 50. How does this affect the imaging and the ability to disappear. Logically, 150s should be much harder to disappear.  The wider baffle is of course to fit an 15 instead of a 9 inch woofer.   The waveguide on the midrange and tweeter do not allow the drivers to depend on the baffle for pattern control;  the dispersion pattern from these drivers is less than 180 degrees.   I have heard the 150s sound as good as 50s but with more low end due to the larger woofer.  Doug Sax, mastering engineer extraordinaire, (now passed) used 150s installed in a soffit to get the ideal, bass is now working into half space instead of full space. So no I don't think this baffle width is a major factor in comparing these two models (although I will ask engineering about it).  In 20_ years I have never had anyone note this or say they can hear this difference.  Rooms are such a major factor influencing imaging and the ability of the  speaker to disappear.  1st reflection problems can dramatically affect this aspect of speaker performance.         

@theophile 

+1 and excellent post.

I have passive 40s V2, driven by an older solid state Musical Fidelity amp. When I got a streamer and a DAC with warmth—in both cases—everything became a little bit tubier. I’m very happy with my system now. You can definitely warm up solid state power with your source and your DAC.

ATC 40A was my first active speaker, 3 years ownership.  Dynamic, fast attack, nice imaging.  Could be an end game transducer.  It's that good.  Moved to ATC 50A.  It is a very different animal.  More of all that's great about the 40A.  It's quite simply in a different league, as it should be.  My end game transducer.

These benefit greatly from Townshend platforms, Furutech DPS 4.1 power cables  and of course everything done properly upstream.

Have fun

I'm leaning toward 150 passives. Part of this hobby is constantly playing and tweaking with components. 

What tube amp would pair well with ATC?  I'm open to integrated as well. I doubt my current 50 and 100W tube amps will do justice on 150. 

I heard the Mcintosh hybrid amps are too slow for ATC.