Are you sure, it is your USB controller that is to blame?
UDMA2-drives like the Samsung or your Benq do not reach their maximum speed when connected to an USB/IDE bridge. If you have an UDMA4 drive available (your Liteon or your Pioneer), you may try these together with your adapters.
I may also connect it to another PC
or install it internally.
I suspect, CD/DVD Speed won't scan either. But you might try Kprobe with your Samsung. Even if connected externally.
In addition, you should remove Adaptec Aspi drivers, if you have installed them.