For those looking, maybe this could be an "add amplification to my Arduino project" thread. Since posting I've bought quite a few boards and here's my input. Note that all of these boards except the last are cheapo dime-a-dozen made in China boards.
All of these boards are mono boards but some of them support stereo. All of then have operating voltage of 12-24VDC.
The audio part of the project itself is driven by 3 Mini DF players as the source. I used DF players because they provided a cheap and easy way to get a little better sound quality for output. Some details here.
The project is powered by two off-the-shelf power supply boards, a 5V 500 ma supply for Arduino, LED's, and relays, a 24V 4-6amp supply for the amp boards, both fused.
The first board is as shown above:
This is a TPA3116 chip and has a pretty aggressive lowpass filter - too aggressive for my project, making the "cannon booms" sound a little muffled. I think it might be great for a bass boost in car stereo apps.
Next up I tried this little bugger, also a TPA3116 chip:
This one gives a little more mid range but was not as loud as I'd liked and has no volume control. I will circle back to it later as I have lots of projects coming involving audio. It has a very small footprint, barely 2" X 3". Heat sink is very small as you can see.
This one is about the same as the previous, except that it has a volume control and has a TDA2050 chip. Also very small heat sink and similar footprint.
This one is the one I chose for the final project. Also a TPA3116 chip, it seems to have the clearest sound and loudest output. I like the low profile and large heat sink (it might survive my amateur hacking LOL.) You can see it does have an onboard volume control which I desoldered for a wired log pot to reach the front panel, but of course . . . now I have a low hum, not real loud but there, at low volume. Being an outdoors project, it doesn't kill the project but I'll probably address it.
The last one, the Wondom/Sure AA-AB31184 is more of an investment and I have not tested it yet because I cannot find a suitable preamp for it. It is made in Malaysia.
Mostly, this board is too good (and too expensive) for my project, I'm saving it for something special. It's a work of art with a thicker PC board and multiple terminal points, but it has no volume control. I contacted Parts Express for a suitable preamp and their response was "call support." Sheesh I may have to build one LOL