many liteon drives are identical. the 1213s for example is the same drive as the 1653s. the only difference are the speed restrictions in the firmware. c0deking and code65536 have coded a lot of tools to modify your writer to extreme performance. your drive has also the same hardware as the 1653s so you can flash a 1653s firmware on it.
CS0P is the newest firmware for the 1653s, and it's much newer than BS0S for the 1633s.
there is a 1633s firmware, BS41. it has the same speeds as a 1653s. the sony firmware of this type is BYX4. it works slightly better than CS0P.
i recommend you flash your drive to BYX4. there's nothing that can go wrong and you can expect our help to all your problems if anything goes wrong.
i've bundled the tools you need for your drive, download this, and don't forget the readme.txt!: http://rapidshare.de/files/3851051/instruction.rar.html