The car runs an 18 volt system. With voltage drop the amp is likely to be seeing 16 volts during the burp. A Z2 will do 8000 watts unclipped at 16 volts and a 1 ohm reactive load. So the sub potentially had 32000 watts on it.
As far as your second question goes: that is a little hard to answer. There are a TON of factors that are involved in putting over 20000 watts to a single sub, and keeping the sub from failing. We were running 24000 watts a peice to our T3 TSNS 18's last year in SS 1-2. The subs themselves were stock. The install is the key factor to keeping the subs alive though. Trying to keep the sub from reaching it's mechanical limits with that much power on it is a nightmare. The subs have to stay linear, or coils will smack the top plate. The cone motion must be kept in check, without developing too much cone pressure, or the cone will fold, but if you don't develop enough cone pressure the sub can bottom out or tear the suspension. So to answer your question, yes some of the SPL subs can handle that much power from the factory, IF they are in the right install.