I am having a similar problem with my SA-8 v2.
I was playing some Mt Eden - Sierra Leonne and after about 4-5 minutes i held my hand infront of the sub and i could feel heat radiating from about an inch away.
I touched the dustcap and it was hot, not warm and if i had to guess it was about 60c the heat was even creaping into the cone on what little is exposed on these subs.
This temp change happened from cold/cool in about 4-5 minutes of playing.
My setup is as follows,
SA-8 v2 D4 wired to 2 ohms in aprrox. 0.6 cubes with a final tuning of about 39hz (prefabbed box, not ideal i know)
I am powering it with an Alpine MRX-M55 (581W @ 2ohm on the cert that came with it)
The settings on the amp are,
Gain - Nominal
Sub Sonic - 24hz
LP filter - 90hz
Bass boost - 1db @ 45hz
I don't really know what to think of all this, not noticing any smells coming from the box either.
What do you figure my problem is? is this an issue to worry about?