I checked the LiteOn website and for the 52x it says that the only difference is that it supports more media. If it had added P-CAV, i am sure they would have mentioned it in the description. It's a pretty quick firmware update, but LiteOn is famous for these.
The 52x firmware R526S07 can be found here -
http://www.liteonit.com/webfw/LTR-52246S/R526S07.zip
And the 48x firmware R48SS09 can be found here -
http://www.liteonit.com/webfw/LTR-48246S/R48SS09.zip
And the site for all other LiteOn firmwares, and their descriptions is -
http://www.liteonit.com/english-load-firmware.htm#cd-rw
I hope LiteOn would add P-CAV RW, as I am sure they have seen the reviews their drives have got and the only area where it doesn't perform upto standards is in the rewriting.