Originally Posted by MichaelJHuman
I don't know much about the Denon. As a general rule, receivers can't match the XPA-5.
First off, the XPA-5 has a transformer with a 1200 VA rating. The Denon is highly unlikely to have a transformer with a rating anywhere near that. The transformer in an amp is one of the primary factors in how much power it can put out.
It has a large amount of capacitance in the power supply (60,000 uF claimed.) I don't know about Denon, but even in high end Yamaha receivers, it's more like two 2000 uF caps. This helps on peaks (some call this ability dynamic headroom.)
It uses 6 transistors / channel (probably two sets of 3 in a Darlington configuration.) More is better in some ways. Probably more reliable with spreading out the load to multiple transistors. It's normal to have only 2 transistors / channel in receivers.
It runs much more heat sink area. It can run cooler. Between that, and having 6 transistors / channel, they can probably run less current limiting than the Denon. The Denon may have to current limit to protect it's transistors, and will run hotter, and closer to it's thermal limits, where it will shut down to try to protect itself.
All of these gives the XPA-5 the advantage near as I can tell, over the Denon. That being said, there's two things to note...
1) If you were not exceeding the Denon's own capabilities, you won't notice an improvement, or much of an improvement with the XPA
2) If you were exceeding the Denon's capabilities, don't expect a massive improvement in unclipped SPL...because you need twice the power for each gain of 3 dB SPL.
I did not notice a big difference going from my Yamaha RX-Z7 only, when I added an XPA-3. But I tend to listen to movies at -10 dB or so, which is 10 dB below reference. The more you push the system, the more likely you would notice the improved power of the XPA.