Help required! Is it worth adding a power amp?

[Woochifer]

Ok, thank you all for your comments and suggestions so far. (Jimmy, has my wife been talking to you?) I would also appreciate some general comments about what you may think is "The weakest link" in the overall system.

The weak link in your system is probably the nonmatching five-speaker setup. From what I know of Meridian speakers, a JBL center speaker could provide a significant enough contrast for you to notice the timbral mismatch. Generally, you're best served by going with as close a voice match all the way around as possible. If the multichannel performance is not your highest priority, then obviously the speaker mismatches will not matter as much as they would to someone else.

Also, your system setup might benefit from the addition of a subwoofer, if for no other reason than to allow you more placement flexibility since main speakers typically locate along the middle of the front wall -- the location in the room where low frequency reinforcement is weakest. And by equalizing the subwoofer to minimize the room-induced peaking and create a more accurate bass, you can extend the range considerably while creating an in-room bass performance that can rival most full-range speakers for considerably less money.

One other point that concerns me is that the Denon does not have a switch to turn off the output to the speakers, so when using an external power amp, the Denon is seeing an open circuit at the speaker terminals. Is this likely to cause any harm?

Doubt that this would cause any harm whatsoever. Can't complete a circuit if the signal path goes nowhere.

I am also still a bit puzzled by why A/V amps are generally not rated for stereo use, so some more explanation of this would help me.

Of course they're rated for stereo use. It just happens that most people who buy them use them more for the multichannel applications. AV amps with an analog bypass for two-channel sources are fine with stereo playback and the 3801 does an analog bypass directly to the amp with no digital conversion when playing two-channel sources with the digital processing switched off. Almost all of the reviewers that I've seen include at least some two-channel playback in the subjective evaluations of AV amps.