While trouble-shooting my installation, I have had the amplifier connected
temporarily in the passenger footwell, where it works very well indeed.
Now that I am ready to install the amp properly in the boot, I am faced
with a grounding dilemma.

So far, I've been using a long, chunky 12V 30A cable supplied with the
amplifier run directly from the battery (in the boot). The amplifier
is connected by a short, equally chunky ground lead to the empeg sled,
which is in turn connected to the relatively flimsy ground lead supplied
by the car for the head unit. Digital playback is excellent, with no
trace of noise, although I do get faint alternator hum on FM (which I
might perhaps become the subject of another post:-).

Now when I move the amplifier in to the boot, I can shorten the 12V
supply cable, which is good, and give it its own grounding point, which
is particularly good since I've not been too happy with using the rather
feeble-looking ground supplied in the centre console anyway. But now,
what do I do about grounding the empeg? From what I've read, it sounds
as if I should take a chunky ground lead from the amplifier to the empeg.
But do I ground at the amplifier end or the emeg end, or both?