Amp Specs esp. DampFactor : Citation, Adcom, etc.

Aewhistory - don't base your decisions on specifications. High DF and low THD, IMD are most likely a result of deep negative feedback that increases TIM (Transient Intermodulation) causing unpleasant bright sound. I would even suspect that sound might be inveresly proportional to spects within given price range. Nothing will replace audition with your speakers. High DF might be not optimum for some overdamped speakers. There are excellent amplifiers with DF=1 (Atmasphere).

Aewhistory,

Amount of gear sold here shows that problem is common. Maybe local dealer will lend you an amp or will let you bring your speakers (my did). Going by spects (especially DF) will be fruitless IMHO. Inductor in series with the woofer limits DF to about 100 anyway.

"we don't measure what is important to the human ear"

Atmasphere - absolutely true but how we can measure it? I don't know how to measure amp's music power or how to measure TIM distortion or how to guarantee synergy with the speakers. Is there anything we can do (new standards) or it will be always black magic?

Aaron - I have Hyperion HPS-938 speakers that have very limited dealership in US. I bought it based on glowing reviews (6 month old dealer demo) without auditioning since I'm in Chicago and the closest dealer is in Pennsylvania. In worst case I would sell speakers but they turned to be absolutely great. Later I found that there is a website of Hyperion users that allow to audition in somebody's home.

I also, being an engineer, tend to over-analyze but I found things much more difficult (black magic?). I would even say that often amp with worse specifications has better sound. It has to do with how these specifications were obtained (negative feedback?) what is synergy with the rest of the system etc.
I tend to read editorial reviews but with a grain of salt. Stereophile reviews are always good and while they don't review non-advertisers they often compare gear. User's reviews and opinions here are great value to me (learning a lot).

I don't have any experience with subs but I'm sure others can help. One thing I noticed that extension is not automatically equal quality. My previous cheaper speakers had two 6" woofers while new ones have two 8" woofers in much larger cabinet but extension is worse (35Hz vs. 32Hz). What got better though, is bass quality - string attack and decay plus better tone and dynamics. I suspect that extension can be forced with extra driver and cross (like 2 1/2 crossover) or tuning of bass refleks. Bass refleks can also be tuned to minimize distortion (current speakers). Bass lower string is 42Hz while piano's is 27Hz but seldom used. For HT it is another story. My TV sound comes thru my system but the main purpose is music. I'm even afraid that sub might screw-up bass definition. There is also money allocation - good subs aren't cheap.

Atmasphere,

As I understand it, our brain works more in time domain than frequency domain. We cannot hear above 20kHz but recent research shows that people can still tell the difference between 20kHz and 50kHz bandwidth listening to music. All spacial clues are also defined by transients.

A lot of this information is lost or changed in digital processing. On one hand it is almost impossible to recover 20kHz sinewave when whole period is defined by two points of 44.1kHz (AFAIK Nyquist criteria protects only frequency information) on the other digital filtering alters step response making ringing to appear after (as it should be)and BEFORE pulse itself. Our hearing is sensitive to the shape of the wavefront. Newest filtering schemes (non-apodizing filters) used, for example, in Meridian CDP have (Stereophile review) normal looking step response and better, more natural sound.

Aewhistory, I had impression that keeping bandwidth well above 20kHz prevents phase shifts within 20kHz but as research suggest it might as well improve transients that our brain processes.

Technical spects have no value to me. I'm not even sure what they mean. Is low THD amp better sounding than high THD amp? Same goes for DF.

Yes, THD should represent a cleaner signal path but the problem is that amp design is a compromise - you want more of this you'll get less of that. THD is usually traded in SS amps for TIM and related odd order harmonics enhancement. Stereophile experimented with Cary CAD-805C amp that has adjustable feedback and found sound to be natural without the feedback (where THD is higher) and "Hi-Fiish" with deep feedback: http://stereophile.com/reference/70/

I'm not sure what can be useful in amps spects. RMS power ratings has some value but I can imagine two amps with the same RMS power rating where one can play music much louder (bigger overhead). It is like trying to classify a taste of wine. I'd like to know if it's red or white, dry or sweet but everything else is very subjective.