Pros: Full array of analog and early digital I/O; Upgradable
Cons: It's old and does not have HDMI or Audyssey
Denon pulled out all of the stops with the AVR-5803A. It even had high resolution digital audio inputs using the proprietary DenonLink 3 (original was a DenonLink2) which allowed DVD-Audio and SACD discs to be transferred digitally (including DSD) to the 5803A.
The AVR-5803A had twelve separate A/V inputs and 3 A/V outputs. Three component video inputs and one component video output were also provided. A remarkable 12 S/PDIF coax/optical inputs were also provided along with S/PDIF outputs. Two sets of 7.1-channel analog inputs were provided which allowed for Blu-Ray lossless audio to be played through the receiver. The receiver even provided bass management on its analog inputs.
The receiver had some of the best DACs of its era and the DACs were 192/24 capable. Smooth sound from all inputs with high quality, high ouput amplifiers that could handle 7 channels easily (the .1 channel doesn't have an amplifier - that's usually found in the sub).
Unfortunately, the list of things that the AVR-5803A did not have that even the most basic receiver now has is growing. The biggest is the lack of HDMI input/ouputs. For a long time, as HDMI matured, the lack of HDMI was a positive. However, in this day it is a clear negative, particulary since all new Blu-Ray players lack component video outputs.
There was also no Audyssey to help "tune" the room. Instead the AVR-5803A had simple audio test tones and with a sound pressure reader, you could balance the room. But, dynamic room equalization is just not possible.
There were some things that modern receivers don't have that the AVR-5803A has. A full LaserDisc input, with a coax AC3 port was including. A phono input was included. And more, switching options than can be easily imagined were included.
The 5803A is built like a tank. Mine was 9 years old and working perfectly when I sold it.
Unforuntately the AVR-5803A was in a long line of Denon receivers that ended with the AVR-5308A (very subtle model number change). No more massive receivers that offer 10 of every type of known input. So, if you can find a good used AVR-5803A and you don't care about HDMI, then by all means take a long look and listen to an incredible receiver for its age!
If this was 2003, the AVR-5803A would get five stars. But in 2013, 1.5 stars have to be removed to cover the lack of capabilities we now take for granted in an AVR. Nothing is wrong with the receiver except time marched on.