The XM-4S has no sense of style, but stealth builds require a certain level of pragmatism, no? This is the smallest amp I can find with enough juice to run high-end components and a sub.

I'm not looking to win any awards, just want it to sound good at 75-80 with the top down.

Are Sony amps a complete joke? In all the posts I've read here, I don't think I've seen any systems that used them. The other smallish amps I'm thinking about are the Boston Acoustics GT-40 and the JL 300/4.

In my experience with home audio, it's hard to tell the difference between great speakers/great amp and great speakers/OK amp. Does the same hold true for car audio?

The price is stealthy too, etronics.com has it for $168.

Sony XM-4S 500W 4/3 Channel Amplifier
-----------------------------------------------
Max Power: 500W
Ad Hoc Power into 4 ohms, (.04% THD): 60W x 4
Ad Hoc Power into 2 ohms, (.1% THD): 60W x 4
Bridged into 4 ohms: 95W x 2 + 250 x 1
Signal to noise ratio (dB): 106
Frequency Response (Hz): 5-100
Input Level Range (V) Line level input: 0.3 - 6
Current Drain at rated output (A): 25
Dimensions (W x H x D): 8-7/9" x 1-5/7" x 7-5/7"
Weight (Approx.): 4.85lb

 

that's a full-range class D like the Alpine PDX amps and does seem
worth a try for a stealth setup. However, the stats you've quoted
above don't match those on Crutchfield, so I'm not sure it really
will have the power you're looking for by itself:
50Wx4 @ 4ohms, 60x4@2ohms
95Wx2 @ 4ohms bridged,
50Wx2 @ 4ohms + 120x1 @4ohms
As for Sony, they are capable of making nice stuff when they want
to, but don't always choose to. Can't speak for this amp, though
I'll be testing out it's mono cousin, the XM-1S, soon.