Studio/Performance Amps for High-End Systems?

A lot of "stage" gear, not necessarily "studio" gear like Crown, QSC and Crest have higher distortion allowances. They are designed for volume and abuse more than quality. Also, the cooling fans in them are usually unbearable for a home system. I've got several at home for my whole house system and they are crude compared to my other gear. Even the connectors are not gold plated and usually are 1/4 jacks or balanced, not RCA.
I'd take my 20 SET tube amp against my 300 watt QSC any day!

I think it tends to be presentation. Every pro amp I have ever had in my systems has been forward and dynamic, but ultimately fatiguing.

With this said, in the right system pro amps do offer a heck of a lot of value.

More expensive amps are more expensive either because...

1) they use better parts/designs, thus cost to manufacture is higher
2) are produced in lower quantities, thus economy of production is a factor
3) are sold by companies that want more profit, so they sell them with higher margins (not a negative thing, nature of capitalism and allowing there to be products for everyone).

Your question is vague, though. When you say "pro" that is not an all encompassing defining label for all people that are "professionals" or make money in the production of music or sound for video/film. Some people would like to equate audiophile being equal to consumer, but that is simply not the case. There are audiophile professionals too.

There are many different factors to consider when quantifying an amplifier's performance, and absolute power output is just 1 factor amongst many. There are functions like THD, slew rate (very important in my mind), and as others have mentioned, heat / noise / efficiency considerations.

Audio equipment has many parallels to the watch. It is a synthesis of functionality and also as a piece of jewelry. Each person can make their own evaluation of what they need and how they will spend it. Some people might need the advanced functions of an aviators chronograph, while others like it just because it looks cool. There is nothing wrong with either viewpoint. Just realize that the line drawn between consumer and professional is more of a marketing demarcation than one of a technical division. Some consumers have become very good listeners and many professionals are much less concerned with accuracy than their target audience - just because of their expertise in engineering pleasant sounding pop/rock for the masses. To say that pro audio equipment is exempt from the "equipment as jewelry" effect is of course just not true.

At the end of the day, you have to make an informed decision as to what equipment to buy based upon its technical merits in your system. This might involve research and testing, or it might be based upon "word of mouth" or following in the footsteps of others... or maybe even based upon one being swayed by glossy advertisements. There are many multitudes of lemmings in both the consumer audio and professional audio markets that fall at all levels of the spectrum of informed / uninformed.

Pro amps like the ones the OP mentioned are designed for power and reliability at the expense of sound quality. They are not "accurate" so much as they are crude, due to the use of lots of negative feedback or digital supplies and output stages. They often have connectivity, controls and features that complicate them compared to amplifiers designed for purity of sound.

In recent years, more and more of the Pro amps run efficient classes of operation such as class D or, when conventional, are biased more toward class B for cooler running and efficiency rather than good sound. In contrast, the most desirable and good sounding audiophile amplifiers run in Class A or are biased toward class A and attempt to minimize or eliminate the use of global negative feedback. Some innovative class D amps have even begun to appear in the audiophile world, but they have not had wide acceptance thus far.

Parts quality in Pro amps tends to be poor when compared with audiophile amplifiers. Pro amps often use generic and inexpensive parts everywhere including critical signal locations. Many audiophile amplifiers have better quality parts in their power supplies than pro models use in the signal path.