Any thoughts on passive v. active speakers?

Building a Line Array of Speakers might be too much to ask of most home users, but if a speaker builder went that route and allowed the home consumer to choose a line sub, a line mid and a line tweet - instead of putting it all in one box, it would provide for upgradeability in the future and unlimited configurations.

Other manufactures might also jump in and provide even more options.

BTW, doing 20hz is not always the most important criteria IMO, for that matter many loudspeakers do that.

Agreed, but as a manufacturer with a need for a reference, while that is not the most important criteria, its not acceptable if the bandwidth isn't there. Our amps go to 2Hz with full power and we want to know what's up when we play them. Plus the bass is really nice :)

In other words, could the "brightness/hardness" effect you point out be a byproduct of the Class AB design that some of the better designers are able to greatly reduce or even eliminate?

'Brightness and hardness' is a product of trace (0.005%) amounts of distortion, often containing the 7th harmonic. The ear is very sensitive to the 7th harmonic as it uses it (and others) as loudness cues to determine how loud a sound is. The ear/brain system converts all forms of distortion into tonality. That is why an amp can sound bright but measure flat on the bench.

I'm thinking about ditching my amps and cables and just buying an active speaker with a balanced input. I have a Krell 2250 and a pair of 140 watt Atma-sphere MA-1MKII. I desperately need speakers and cables, but not sure if I want to go through the bother (and expense) of finding the perfect matching set.

Should I go with a speaker & amp that are already matched or keep building my system like a bespoke smorgasbord?

Pragmatically it comes down to the implementation of either way more than the inherent virtues of one "principle" alone. On paper the advantages of active (+ DAC/DSP) speakers are rather obvious and appeals to me a lot, and I would indeed love to go that route should the right (speaker-)combination come along (this is a tempting solution, but too expensive for my wallet I'm afraid: http://hometheaterreview.com/meyer-sound-x-10-powered-loudspeakers/), but for now the right speaker-part of the active combo evades me.

All things being equal, and at the present DSP-technological state, I'd rather avoid passive cross-overs altogether; going radical about it one could pursue an alternative DIY-solution with the passive speakers fitting ones sonical bill and wreck them apart, more or less - at least as a means to by-pass the passive cross-over, connect each driver to their dedicated amp-channel, and let a DSP handle the cross-over duties. I've heard this conversion (from passive to active DSP) go extremely well in setup of a friend of mine, to the point really where there's no comparison, but it takes skill and patience to get there. Perhaps the active solution is much more of an obvious, preferred choice with cheaper solutions where incredible value can be had in such all-in-one systems (see JBL LSR 305/308, among many others).

Have stood at the crossroad of active or passive myself, the former from an outset with my existing speakers, but have chosen to go the latter route based on new, upcoming and highly sensitive speakers (~106-107dB's). I believe both paths would've been exhilarating to try out though - if only one could've. Merging other product categories seems more prudent here, like DAC and preamp for example, and focusing solely on one source (digital, in this case) to max out the fullest potential with the financial means available.

Finally then: in your case I'd seek out some potential active and/or otherwise combined solutions, listen to them closely where possible and preferable, and see whether the totality of sonic impressions go beyond that which passive, "discrete" solution can muster. You may find youself surprised, one way or the other.

" if a speaker builder went that route and allowed the home consumer to choose a line sub, a line mid and a line tweet - instead of putting it all in one box, it would provide for upgradeability in the future and unlimited configurations. "

Upgrade-ability and unlimited configurations can only promise changes, and not better sound quality.

I will probably get wonked on the head for saying this, but I'm going to make this argument anyway:

A Line Array of speakers is more efficient and makes better use of the amplifier than non-arrayed speaker. Sonic qualities aside the main job of an amp is to move drivers which push air.

Most class A amps convert their power into heat. The bigger the line array, the more the amp can breath and do its job which isn't heating your room.

At every power level you will hear more and appreciate your amp and music more as your line array get bigger.