Receivers are the Swiss army knives of audio components. They do almost everything except move air. Long shunned by audiophiles for their inferior sonic quality, receivers of late have been gaining ground on their separate component cousins.
One large reason for this is the increasing prevalence of digital in the audio chain. Receivers are typically made by large companies with the resources to take on digital engineering and do it right. Getting it right in digital in a mass produced product does not cost nearly as much as it does in analog.
Conversely, the smaller high end companies are typically well grounded in the analog domain and making the switch to, or integrating digital research and engineering into their operations is virtually impossible on an economic basis. How much it cost Texas Instruments to develop their digital amp chips isn't known but but Donald Trump could probably retire on it. Other chip companies have spent upwards of $30 million with no marketable result.
The Panasonic receivers use the TI chipset resulting in the sound quality/price ratio we were trumpeting several years ago. Once the chipset has been developed, it still takes a major player (Panasonic/Matsushita with over 250,000 employees) to incorporate a complete digital product offering.
Other large companies such as Sony and Yamaha now have digital amp receivers with digital chipsets of their own while some companies use Tripath or ICE (by B&O amplifier modules. The net effect is to give them a big boost in closing the huge gap in sound quality between themselves and the best of the separate component manufacturers. Pioneer has chosen to stay with analog amps and upped it’s game by sensing the temperature of each output transistor and adjusting the bias accordingly.
Onkyo (and Integra) has long been the standard by which receiver amplifier sections have been measured but the truth is the top end models of many brands sound extremely good.
Besides the fidelity of the basic signal, the other well developed area of interest for audiophiles is room correction. Taking the major room problems out of the equation is a huge step forward for overall audio performance. There has been a price to pay for this in terms of transparency in the past but with each new implementation, this seems to fade more into the distance. The Audyssey system now incorporated in many receivers has worked extremely well in the systems we've worked with and there has been no sacrifice in transparency.
Good room correction has been very expensive to do in the past and perhaps the top end systems are better but any improvement will cost a great deal more. Lyngdorf, Meridian, Tact, DEQX and Rives are about it for the high end and going with any of these equipment makers will add many thousands of dollars on to the total cost of your system.
Small note. The greatest benefits of room correction have always been in small to medium sized rooms. In very large rooms or rooms with large openings, any room correction system has increasing trouble with the increasingly long reverberation times. This is the case with most systems but the Pioneer does address this in their system - allowing for time sensitivity to be varied.