My drive is manufacturered in China, started out with firmware D.LC. After seeing
AtlantaDutchman's success, I AGAIN tried to flash the 52X firmware, again without success. A bit of snooping around brought me to
this page at cdfreaks.com..
marschw at cdfreaks deserves the credit for how to hack the firmware I'm linking below, although his post about the edit/change is backwards, the "K' needs changed to "D", and the file I link is mod from the newest firmware offered for the 5224P, "KSC.EXE", not the older firmware on the cdfreaks page. However, this firmware upgrade does NOT add Mt. Rainier support AFAICT, I think the reason is that the China-manufactured drives use the older Mediatek chip, though this is just something I vaguely recall reading, might be incorrect.
Anyway, I successfully upgraded my drive to the 52X with this modded firmware and it works "as well as before". Note from the cdfreaks forum page that you might not be able to flash back to the old version again, it's one of those
TRY AT YOUR OWN RISK situations.
52X Firmware 5224P Mod for China - D.x.C drives
REEDIT: My drive barely works when set to cable select on two different motherboards, both before and after the firmware update. When the drive is set to SLAVE it works without the "issues" of lockup on CDSpeed. The firmware update does work, the drive reads and writes over 48X, though without Mt. Rainier support it's of limited benefit to upgrade the firmware just to bump it from 48X to 52X, especially with the media being more likely to introduce errors at these higher speeds.