The only tests I've found only show 16-24 Ultra speed
http://www.liteonit.com/ODD/English/e_product/e_sohw1213s.asp - according to this, the drive supports ALL the CD-RW standards, including low speed 1x/2x/4x
High speed had a standard of 4-10x for a long time, I suspect that 12x is a bit of an afterthought, although Liteon's CD-RW drives with later chipsets supported HS at a maximum of 12x - and other makers with the same chipsets did 16x - on HS media!
If you are burming, rather than UDF formatting, turning Smart-Burn off may enable 12x, but if Smart-Burn is holding the speed down, that means it does not rate the media highly enough.
PS. Using the official firmware update ONLY, should not give rise to any warranty problems, and the drive needs improvement - current firmware is TS0D, with TS0C and TS09 (you don't need them) inbetween.
These drives are getting a very poor reputation, and even loyal Liteon hackers are beginning to despair - the 812/832 is still a better drive than the 1213S - so far, Liteon have made a 12x and 16x that really cannot burn decently at those speeds, while experimenting on the paying public, with their new chipset.